Also add this path to .gitignore to prevent future mistakes.

The main purpose of this change is to avoid a problem where new golden
files added to certain directories for test purposes (like .log)
shouldn't be ignored.

Cleaning up a bit more and broadening the definition, this removes
ignore rules for artifacts of Terraform itself (state files, plans).
It's generally not recommended to be using this codebase as your
Terraform working directory anyway; build here, test elsewhere.

The "terraform" provider was previously split out into its own repository,
but that turned out to be a mistake due to how tightly it depends on
aspects of Terraform Core.

Here we prepare to bring it back into the core repository by reorganizing
the directory layout to conform with what's expected there.

These files are already included in the bundle

Allows for managing organization membership, teams, team membership, and
team repositories.

 * Remove `make updatedeps` from Travis build. We'll follow up with more
   specific plans around dependency updating in subsequent PRs.
 * Update all `make` targets to set `GO15VENDOREXPERIMENT=1` and to
   filter out `/vendor/` from `./...` where appropriate.
 * Temporarily remove `vet` from the `make test` target until we can
   figure out how to get it to not vet `vendor/`. (Initial
   experimentation failed to yield the proper incantation.)

Everything is pinned to current master, with the exception of:

 * Azure/azure-sdk-for-go which is pinned before the breaking change today
 * aws/aws-sdk-go which is pinned to the most recent tag

The documentation still needs to be updated, which we can do in a follow
up PR. The goal here is to unblock release.

Seems like Emacs is generating .test files when saving _test.go files -
we don't need these in the repo.