Make update_status use synchronized_zone
There is a race condition when adding a new recordset to a zone
and when central is processing the update_status from a previous
recordset/zone operation. In the subsequent recordset operation,
central fails to update the zone's action/status in DB to UPDATE/PENDING.
It remains as NONE/ACTIVE, and worker error's out.
Each operation retrieves a different copy in memory of the Zone object
(when it calls self.storage.get_zone). As a result this does not update
the obj_changes field for the zone object for the latter operation.
Therefore the DB update doesn't update any values.
update_status should be synchronized as it updates zone DB