Reads all message handler requests from the database.

def ReadMessageHandlerRequests(self):
    """Reads all message handler requests from the database."""
    res = []
    leases = self.message_handler_leases
    for requests in itervalues(self.message_handler_requests):
      for r in itervalues(requests):
        res.append(r.Copy())
        existing_lease = leases.get(r.handler_name, {}).get(r.request_id, None)
        res[-1].leased_until = existing_lease

    return sorted(res, key=lambda r: -1 * r.timestamp)