Get kafka notifications to work with kafka-python 0.9.5

* poll() now returns empty list instead of None
* metadata_broker_list has been dropped, there's a new
  bootstrap_servers
* Add a LOG.debug() for the actual message

python simulator.py -d DEBUG --topic notifications.info --url kafka://localhost:9092 notify-server
python simulator.py -d DEBUG --topic notifications --url kafka://localhost:9092 notify-client -m 1000 -w 1

More tips:
http://kafka.apache.org/documentation.html#quickstart
https://www.digitalocean.com/community/tutorials/how-to-install-apache-kafka-on-ubuntu-14-04

Depends-On: Ia324b4c89b05c536708baf7950857cd159578cec
Change-Id: I80911d2678ea5e8d0cd6b146a1e29a58858e3144

oslo_messaging/_drivers/impl_kafka.py

@@ -228,8 +228,7 @@ class Connection(object):
     def declare_topic_consumer(self, topics, group=None):
         self.consumer = kafka.KafkaConsumer(
             *topics, group_id=group,
-            metadata_broker_list=["%s:%s" % (self.host, str(self.port))],
-            # auto_commit_enable=self.auto_commit,
+            bootstrap_servers=["%s:%s" % (self.host, str(self.port))],
             fetch_message_max_bytes=self.fetch_messages_max_bytes)
 
 
@@ -262,6 +261,7 @@ class KafkaListener(base.Listener):
                 messages = self.conn.consume(timeout=timeout)
                 for msg in messages:
                     message = msg.value
+                    LOG.debug('poll got message : %s', message)
                     message = jsonutils.loads(message)
                     self.incoming_queue.append(OsloKafkaMessage(
                         ctxt=message['context'], message=message['message']))

oslo_messaging/tests/drivers/test_impl_kafka.py

@@ -284,4 +284,4 @@ class TestWithRealKafkaBroker(test_utils.BaseTestCase):
         deadline = time.time() + 3
         received_message = listener.poll(timeout=3)
         self.assertEqual(0, int(deadline - time.time()))
-        self.assertIsNone(received_message)
+        self.assertEqual([], received_message)