reorganize placeholder data call to live with provisioner implementation; force users to use the generated function, therefore forcing validation, for all variables except winrmpassword, by doing a simple string check against the placeholder data.

* Move setting of default EnvVarFormat to the Prepare function
* Add generated hcl2 structure for the updated Shell provisioner config
* Move `EnvVarFormat` field to shared common shell type
* Add description for the `env_var_format` parameter
* Update `env_var_format` when used with `use_env_var_file`

It is simply the best/simplest solution and trying to prevent users from passing and integer here would be like opening a can of worms. Because:

* we cannot make mapstructure validate our duration string ( with an UnmarshalJSON func etc.)
* we cannot make mapstructure spit a string instead of a duration and packer will decode-encode-decode config.
* the hcl2 generated code asks for a string, so this will be enforced by default.

Before this commit it was possible to set a duration using an integer or a float. Go's time.Duration is an int64 internally an mapstructure will take advantage of this and load the number as a int64 but `1` means one ns which is unexpected/confusing. To avoid confusion and enforce readability this forces users to pass a string with a unit for a duration; ex "56s".

for history

* make possible execution policy values lowercase
* prefix execution policies possibilities

this has the effect to not wrap the command, which will allow to know the exit status of a command in docker

* I had to contextualise Communicator.Start and RemoteCmd.StartWithUi
NOTE: Communicator.Start starts a RemoteCmd but RemoteCmd.StartWithUi will run the cmd and wait for a return, so I renamed StartWithUi to RunWithUi so that the intent is clearer.
Ideally in the future RunWithUi will be named back to StartWithUi and the exit status or wait funcs of the command will allow to wait for a return. If you do so please read carrefully https://golang.org/pkg/os/exec/#Cmd.Stdout to avoid a deadlock
* cmd.ExitStatus to cmd.ExitStatus() is now blocking to avoid race conditions
* also had to simplify StartWithUi

this regroups the calls of tmp func calls into one package.
the tmp pkg allows to store tmp files under a common directory for easier managment

Squashed commit of the following:
commit 74b674c01560c6b547e9cab5e8afb486f0fe7d6c
Merge: fc94b5714 66001525d
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Fri Nov 2 02:02:38 2018 -0400

    Merge branch 'remove_TMPDIR_docs' of github.com:tb3088/packer into remove_TMPDIR_docs

commit fc94b571428447aaf2e5171967c95cdf9e5c73ff
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Fri Nov 2 01:42:38 2018 -0400

    update tests to honor configured temporary directory

commit 5a562359f4937af506607dd96ed1c46426093f52
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Thu Nov 1 18:52:38 2018 -0400

    sync straggler to refactor. implement tests at packer/configfile instead of buried in docker.

commit 9d5a4a0935bfd049e2f8f50ad73e4455b42c9410
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Thu Nov 1 15:39:46 2018 -0400

    insert URL to GoLang API for os.TempDir()

commit fbae4c2e051898aecd8705e9d8a20353430ede23
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Thu Nov 1 07:41:29 2018 -0400

    revise documentation to match code

commit 3590fae8bd0afa92a161a49ed794ee32e357d583
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Thu Nov 1 07:21:59 2018 -0400

    refacter config_file. replace all hard-coded os.TempDir with wrapper

commit d5c5306a97b648ded06a8eb76ce728f07c9924f0
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Wed Oct 31 20:11:36 2018 -0400

    close massive file overwrite hole with TempDir

commit 0a72297da86089fbd07e4f7d9472a92fa4d1c733
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Wed Oct 31 01:06:00 2018 -0400

    adjust var declaration scope

commit 20f68228b6c372d984ea5b055cfc8bda9b110ac5
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Wed Oct 31 00:54:35 2018 -0400

    use mktemp() equivalent to create temporary directory

commit c73ebe3d8321664a2685a0baa8e441dd895b0db4
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Tue Oct 30 20:40:58 2018 -0400

    remove extraneous variable declaration, fix FOR loop

commit 63549b8bd745a0090b15ed0b0ebf644162db27db
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Tue Oct 30 19:30:44 2018 -0400

    match styistic convension with rest of docs

commit 976101074942db36f10d3a686d6d29ddb7c01926
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Tue Oct 30 19:08:39 2018 -0400

    revert dangling config file change

commit 95159afbc05eac96ed11c3183af5fb0abe2f2d5c
Author: Matthew Patton <matthew.patton@itgfirm.com>
Date:   Fri Dec 29 23:53:43 2017 -0500

    replace invalid TMPDIR variable wth PACKER_TMP_DIR.
    update ConfigTmpDir() to try common temporary paths first and
    only write to configDir() as a last resort.

commit 66001525d72de56a4cf9339b900c46f59bc6e91a
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Fri Nov 2 01:42:38 2018 -0400

    update tests to honor configured temporary directory

commit e9b6adefeae8c65eb8aa47fef38cbf0aa424338c
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Thu Nov 1 18:52:38 2018 -0400

    sync straggler to refactor. implement tests at packer/configfile instead of buried in docker.

commit 852113ed076e2d14e5dca6815ea680da1e2896bb
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Thu Nov 1 15:39:46 2018 -0400

    insert URL to GoLang API for os.TempDir()

commit 54add38d1d1c6e283cd444b367ed8bd49a5f3699
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Thu Nov 1 07:41:29 2018 -0400

    revise documentation to match code

commit 6b5b8f6d4edad0e187ca13d64ac4118f34eee643
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Thu Nov 1 07:21:59 2018 -0400

    refacter config_file. replace all hard-coded os.TempDir with wrapper

commit c22092c601c33484327674f322c7379fa41506d7
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Wed Oct 31 20:11:36 2018 -0400

    close massive file overwrite hole with TempDir

commit 7a730450916bf8e5dbc2a741ec233a49466ab7cc
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Wed Oct 31 01:06:00 2018 -0400

    adjust var declaration scope

commit 0f2933adb6f6922dfeab78a95371a444ec8918ab
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Wed Oct 31 00:54:35 2018 -0400

    use mktemp() equivalent to create temporary directory

commit d74839ede05dacf712b55a7bb48aec19fe6b007f
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Tue Oct 30 20:40:58 2018 -0400

    remove extraneous variable declaration, fix FOR loop

commit eb65416619437e4a3dec90277770803dd5b2281c
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Tue Oct 30 19:30:44 2018 -0400

    match styistic convension with rest of docs

commit acaa2b31ed463219c4ef099f351eec72406e2989
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Tue Oct 30 19:08:39 2018 -0400

    revert dangling config file change

commit e573fde668dcb418561e61535c1d68b2888f5b0f
Author: Matthew Patton <matthew.patton@itgfirm.com>
Date:   Fri Dec 29 23:53:43 2017 -0500

    replace invalid TMPDIR variable wth PACKER_TMP_DIR.
    update ConfigTmpDir() to try common temporary paths first and
    only write to configDir() as a last resort.

commit 39a9874afc9dea71b36753375fb7feb61ffecf69
Merge: 8a413cfe8 3315812c
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Tue Oct 30 18:19:26 2018 -0400

    Merge branch 'master' of https://github.com/hashicorp/packer into prestine

commit 8a413cfe83b0a70dbd99c32d936334ca5788ca9b
Merge: e07491de5 4e14710a
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Mon Oct 1 20:18:10 2018 -0400

    Merge remote-tracking branch 'upstream/master' into prestine

commit e07491de59cead0b337a7f57f4a6c625e1f560ab
Merge: 42610a35d a1fa35df
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Tue Aug 21 13:26:19 2018 -0400

    Merge remote-tracking branch 'upstream/master' into prestine

commit 42610a35d5ef65af8844a58ad70e2ec75262da6a
Merge: 5298142da 0d63cf7b
Author: Matthew Patton <matthew.patton@itgfirm.com>
Date:   Tue Jun 19 22:45:05 2018 -0400

    Merge remote-tracking branch 'upstream/master' into prestine

commit 5298142da6da95354844f201deeeef3c599e48b2
Merge: 7bb110bc7 9d973655
Author: Matthew Patton <mpatton@enquizit.com>
Date:   Mon Jun 11 15:10:09 2018 -0400

    Merge remote-tracking branch 'upstream/master' into prestine

commit 7bb110bc744c9797fcaec25a265d9b85a22d6d6b
Merge: a61c869ca 6189d66e
Author: Matthew Patton <matthew.patton@itgfirm.com>
Date:   Wed May 9 23:41:22 2018 -0400

    Merge remote-tracking branch 'upstream/master' into prestine

commit a61c869ca7268acf0e3b1e1fa7a8ee7feea65984
Merge: 098101dd9 4be5f072
Author: Matthew Patton <matthew.patton@itgfirm.com>
Date:   Fri May 4 10:13:04 2018 -0400

    Merge remote-tracking branch 'upstream/master' into prestine

commit 098101dd99f08b0ca110d33eff6904537c6d21de
Merge: fefaf0fa 554b2b4a


Author: Matthew Patton <matthew.patton@itgfirm.com>
Date:   Tue May 1 20:52:30 2018 -0400

    Merge branch 'EOL-handling' into prestine
Co-Authored-By: Matthew Patton <pattonme@yahoo.com>

Use the common elevated code instead.

Fixes #6104

explicitly use set-variable to work around a bug some users saw where the command invocation would vail

Going to revert this change for now, becuase of potential issues that arise from calling Prepare() twice
Revert "use statebag instead of SetSharedState for winRM password"

This reverts commit b35acbd8.

filter winrm password from logs
Add new root-level packer template option, sensitive-variables, to tell us what user variables to mark sensitive.

* Dollars are interpreted by *nix shells so paths using env vars such as
  ${env:SYSTEMROOT} will cause issues

Previously the location the file was uploaded to was set internally and
used ${env:SYSTEMROOT}/Temp as the destination folder.
By default, in order to inject the required environment variables, the file
is 'dot sourced' by the 'execute_command' using the {{ .Vars }} variable.
Unfortunately the inclusion of the dollar in the path caused issues for
users connecting over ssh as the (typically bash) shell running the execute
command would try and interpret the dollar sign.
The change allows users to specify the location the file is uploaded to,
thereby allowing the user to specify a custom 'execute_command' that
escapes any dollar signs that could be present in the path.
If not set the upload path now defaults to using C:/Windows/Temp as the
upload folder.

use build name to ensure that winrm password and other shared state is not overwritten if two builders need the password in the same packer run.