This prevents Terraform from crashing on apply/destroy with a directory
with no Terraform configuration files. We allow a destroy with no files
but not an apply.
Have the defer'ed State.Unlock call append any error to the
RunningOperation.Err field. Local error would be rare and
self-correcting, but when the backend.Local is using a remote state the
error may require user intervention.
The local backend implementation is an implementation of
backend.Enhanced that recreates all the behavior of the CLI but through
the backend interface.
Mitchell Hashimoto