R1:892a9a1f07d9

Make cluster repositories more resistant to freezing

Summary:
Ref T10860. This allows us to recover if the connection to the database is lost during a push.

If we lose the connection to the master database during a push, we would previously freeze the repository. This is very safe, but not very operator-friendly since you have to go manually unfreeze it.

We don't need to be quite this aggressive about freezing things. The repository state is still consistent after we've "upgraded" the lock by setting…