Make sure mongorestoring user/role data doesn't interfere with ongoing user or role modifications

If you use mongorestore to restore user or role data, those updates could conflict with other user or role management operations going on in the cluster.
Mongos uses a distributed lock to prevent user modifications performed on one mongos from conflicting with modifications from another mongos, while mongod uses a mutex. We should acquire the same lock that the user management commands do whenever mongorestore is restoring user/role data to prevent conflicting writes.

Proposed way to do this is to introduce two new commands: lockAuthzUpdateLock and unlockAuthzUpdateLock, and use them in mongorestore.