Add docs for Terraform remote state

[sehqlr]

A question about support for terraform remote state came up in the mantl gitter channel. As of right now, terraform doesn't support loading in remote tfstate files. Should it? And if the answer to that question is no, should we add some documentation to the README about how to use remote state files in the workflow?

[BrianHicks]

It could. When Terraform uses remote state storage, it stores a local copy in .terraform/terraform.tfstate or similar. That seems a bit like a hack to use though, no guarantee that it'd be there.

[sehqlr]

I was looking at this question again, and Terraform syncs remote and local state, so we don't need to support this explicitly. We should add documentation for loading in the remote state directly with --root, though

[sean-abbott]

I believe terraform does not necessarily include all of the state locally anymore (at least past 0.9.0). In order to deal with that, as well as a few other things, I've made the changes now merged into master on my fork (https://github.com/sean-abbott/terraform.py)

If you'd like to take it for a spin and see if it works for you, I'd appreciate it. Note the differences in installation, and that the tool is now called "ati" for "ansible terraform inventory".

[abra7134]

I think for support of remote storages better to use the 'terraform state pull' command which receives the current .tfstate not important local it or remote.

[sean-abbott]

fair point.

[sean-abbott]

So...I've updated the PR to use terraform state pull instead of any kind of manual remote fetching, with an option to fall back on the old reading of the local files. What do you think?