title: Kafka client poll() throws EOFError after each received message
body: <p>I am using a slight variant of the example client polling code I found in the <a href="https://github.com/confluentinc/confluent-kafka-python/blob/master/examples/consumer.py" rel="nofollow noreferrer">Confluent github</a>:</p>
  
  <pre><code>c = Consumer({'bootstrap.servers':'localhost:9092','group.id':'devops','auto.offset.reset':'earliest'})
  c.subscribe(['system-diskio-write-bytes','system-cpu-user-pct'])
  
  try:
      while True:
          msg = c.poll(timeout=1000.0)
          if msg is None:
              continue
          if msg.error():
              print(msg.error())
          else:
              print('topic: %s key: %s value: %s' % (msg.topic(), msg.key(), msg.value()))
  
  except KeyboardInterrupt:
      print('Polling interrupted by consumer')
  </code></pre>
  
  <p>The EOF KafkaError is raised after every received message:</p>
  
  <pre><code>topic: system-diskio-write-bytes key: None value: b'{"route" : "system-diskio-write-bytes", "timestamp" : 2019-03-06T13:46:25.244, "value" : 655002980352.0}'
  KafkaError{code=_PARTITION_EOF,val=-191,str="Broker: No more messages"}
  </code></pre>
  
  <p>I don't understand why this happening--any ideas as to why this error is being thrown how to fix? Any ideas are much appreciated--thanks!</p>