The backend state tests weren't properly checking for persistence.
Update the test to persist states and fetch them again from the backend,
checking that lineage is preserved.
This adds a "lock" config (default true) to allow users to optionally
disable state locking with Consul. This is necessary if the token given
doesn't have session permission and is necessary for backwards
compatibility.
Backends are a mechanism that allow abstracting the behavior of
Terraform CLI from the actual core. This allows us to slip in special
behavior such as state loading, remote operations, etc.
James Bardin