To avoid subtle races when destroying a cluster, we need to make
sure that the cluster destroy LU is the last LU ever executed.
That LU gets the BGL exclusively; however, it needs the daemons
for it to proceed, so the daemons will still be running at its
finish, thus causing the race. (Also note, that the watcher might
restart stopped daemons at any time.) Therefore, the last thing
that LU will do is to transfer the BGL to WConfD itself; WConfD
will also modify the configuration to a no-master state, thus
making sure it will refuse to restart.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>