Added locking support via blob leasing (requires that an empty state is
created before any lock can be acquired.
Added support for "environments" in much the same way as the S3 backend.
Move the Swift State from a legacy remote state to an official backend.
Add `container` and `archive_container` configuration variables, and deprecate `path` and `archive_path` variables.
Future improvements: Add support for locking and environments.
Move the S3 State from a legacy remote state to an official backend.
This increases test coverage, uses a set schema for configuration, and
will allow new backend features to be implemented for the S3 state, e.g.
"environments".
James Bardin