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.

Rather than using reflection to grab the whole SSH config, for now just use the config convenience functions to get the majority of needed values

generated func now validates based on data provided in context, which needs to include the future values if it is to be interpolated properly.

Creates a final "cleanup" provisioner to run if an error occurs during a provisioning step, allowing users to perform any custom cleanup tasks that must happen on the VM before the VM is shut down and destroyed.

we have to as it is what calls our provisioners

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.

`find . -type f -name '*.go' -not -path "./vendor/*" -exec goimports -w {} \;`

Run now takes a context as well as a statebag. We'll assign the context
to the blank identifier to prevent namespace collisions. We'll let the
step authors opt-in to using the context.

`find . -iname "step_*.go" -exec gsed -i'' 's/func \(.*\)Run(/func \1Run(_ context.Context, /' {} \;`

gomvpkg -from "github.com/mitchellh/multistep" -to "github.com/hashicorp/packer/helper/multistep"