[hbck2] AMv2 Lock Picker

This issue is about adding a lock picker to the HbckService

Over the w/e I had interesting case where an enable failed – a subprocedure ran into an exclusive lock (I think) – and then the parent enabletabled tried rollback. The rollback threw CODE-BUG because some subprocedures were in unrollbackable states.... so we ended up skipping out of the enable table procedure. The enable table procedure was marked ROLLBACKED... so it got GC'd. But the exclusive lock it had on the table stayed in place.

The above has to be fixed but for the future, we need way to kill locks otherwise only alternative if removing master proc wal files – which is a bigger pain restoring good state.