- Currently the disable_checkpoint setting from $HOME/.terraformrc is never
respsected due to:
-- The runCheckpoint go routine being fired off prior to loading configuration
-- The config.Merge method not actually merging in the c2s settings

Implement debugInfo and the DebugGraph

DebugInfo will be a global variable through which graph debug
information can we written to a compressed archive. The DebugInfo
methods are all safe for concurrent use, and noop with a nil receiver.
The API outside of the terraform package will be to call SetDebugInfo
to create the archive, and CloseDebugInfo() to properly close the file.
Each write to the archive will be flushed and sync'ed individually, so
in the event of a crash or a missing call to Close, the archive can
still be recovered.

The DebugGraph is a representation of a terraform Graph to be written to
the debug archive, currently in dot format. The DebugGraph also contains
an internal buffer with Printf and Write methods to add to this buffer.
The buffer will be written to an accompanying file in the debug archive
along with the graph.

This also adds a GraphNodeDebugger interface. Any node implementing
`NodeDebug() string` can output information to annotate the debug graph
node, and add the data to the log. This interface may change or be
removed to provide richer options for debugging graph nodes.

The new graph builders all delegate the build to the BasicGraphBuilder.
Having a Name field lets us differentiate the actual builder
implementation in the debug graphs.

When trying to use a debugger, you don't want the terraform to run in a
new child process. Setting TF_FORK=0 will skip panicwrap and continue
running the program in the current process. This will also give direct
access to log output, and stdout.

Also added documentation explaining what happened and how to fix it

This introduces the terraform state list command to list the resources
within a state. This is the first of many state management commands to
come into 0.7.

This is the first command of many to come that is considered a
"plumbing" command within Terraform (see "plumbing vs porcelain":
http://git.661346.n2.nabble.com/what-are-plumbing-and-porcelain-td2190639.html).
As such, this PR also introduces a bunch of groundwork to support
plumbing commands.

The main changes:

- Main command output is changed to split "common" and "uncommon"
  commands.

- mitchellh/cli is updated to support nested subcommands, since
  terraform state list is a nested subcommand.

- terraform.StateFilter is introduced as a way in core to filter/search
  the state files. This is very basic currently but I expect to make it
  more advanced as time goes on.

- terraform state list command is introduced to list resources in a
  state. This can take a series of arguments to filter this down.

Known issues, or things that aren't done in this PR on purpose:

- Unit tests for terraform state list are on the way. Unit tests for the
  core changes are all there.

This brings in the go-colorable library when running on Windows in order
to output console colors correctly instead of leaving the codes in place
as is currently the case.

We weren't doing any log setup for acceptance tests, which made it
difficult to wrangle log output in CI.

This moves the log setup functions we use in `main` over into a helper
package so we can use them for acceptance tests as well.

This means that acceptance tests will by default be a _lot_ quieter,
only printing out actual test output. Setting `TF_LOG=trace` will
restore the full prior noise level.

Only minor behavior change is to make `ioutil.Discard` the default
return value rather than a `nil` that needs to be checked for.

Seems to be a refactoring leftover of some kind as on lines 146-148
these calls are done again…

/cc @pearkes @armon - exe dir and pwd