Allow alternate directory for state/ folder

[drnic]

Currently the state of which infrastructure/systems/configuration have been selected are stored within the project's state/ folder.

To allow users to have multiple deployments, or to allow them to commit their state/ folder to a git repo outside of this git repo, we should allow an alternate state folder to be provided by env var.

For example https://github.com/starkandwayne/bucc/blob/master/bin/bucc#L17