During backend initialization, especially during a migration, there is a
chance that an existing state could be overwritten.
Attempt to get a locks when writing the new state. It would be nice to
always have a lock when reading the states, but the recursive structure
of the Meta.Backend config functions makes that quite complex.
Previously when runnign a plan with no exitsing state, the plan would be
written out and then backed up on the next WriteState by another
BackupState instance. Since we now maintain a single State instance
thoughout an operation, the backup happens before any state exists so no
backup file is created.
This is OK, as the backup state the tests were checking for is from the
plan file, which already exists separate from the state.
The old behavior in this situation was to simply delete the file. Since
we now have a lock on this file we don't want to close or delete it, so
instead truncate the file at offset 0.
Fix a number of related tests
Having the state files always created for locking breaks a lot of tests.
Most can be fixed by simple checking for state within a file, but a few
still might be writing state when they shouldn't.
James Bardin