Fixes#12871
We were forgetting to remove the legacy remote state from the actual
state value when migrating. This only causes an issue when saving a plan
since the plan contains the state itself and causes an error where both
a backend + legacy state exist.
If saved plans aren't used this causes no noticable issue.
Due to buggy upgrades already existing in the wild, I also added code to
clear the remote section if it exists in a standard unchanged backend
When migrating from a multi-state backend to a single-state backend, we
have to ensure that our locally configured environment is changed back
to "default", or we won't be able to access the new backend.
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.
Mitchell Hashimoto