'Send a message to another cell by JSON-ifying the message and
making an RPC cast to \'process_message\'.  If the message says to
fanout, do it.  The topic that is used will be
\'CONF.rpc_driver_queue_base.<message_type>\'.'

def send_message_to_cell(self, cell_state, message):

    topic_base = CONF.cells.rpc_driver_queue_base
    topic = ('%s.%s' % (topic_base, message.message_type))
    cctxt = self._get_client(cell_state, topic)
    if message.fanout:
        cctxt = cctxt.prepare(fanout=message.fanout)
    return cctxt.cast(message.ctxt, 'process_message', message=message.to_json())
