Catch the case when no new messages are available

Confluent Kafka client throws the KafkaError._PARTITION_EOF exception
when no new messages are available in a given partitiion. We should
catch this case and continue consuming after a short sleep.

Story: 2003705
Task: 30116
Change-Id: I44add24df764bbc4e718358a8af75903e035f3f0

monasca_common/confluent_kafka/consumer.py

@@ -70,6 +70,10 @@ class KafkaConsumer(object):
                 continue
             elif not message.error():
                 yield message
+            elif message.error().code() == \
+                    confluent_kafka.KafkaError._PARTITION_EOF:
+                time.sleep(0.1)
+                continue
             else:
                 log.error("Kafka error: %s", message.error().str())
                 raise confluent_kafka.KafkaException(message.error())