This change fixes two bugs:
1. A dead-lock that occurs between osrm-datastore and libosrm when an
old dataset is free during a data update. This happened because the
mutexes where acquired in a different order.
2. A region is deleted eventhough it is still in use. This happens when
libosrm gets overtaken by osrm-datastore, so the new dataset is in
the same region the old one was.