EMQX benchmark QoS 2 issue

[bmaidics]

EMQX benchmark doesn't wait for the PUBREC before closing the tcp connection. Zilla is waiting for the incomplete offsetcommit to be acked (offset commit response), but the tcp server got closed -> Zilla closes the publish stream.
This causing qos2 messages published vie EMQX benchmark tool to not arrive into Kafka.

Furhter notes:

Zilla is sending offsetCommitIncomplete at mqttData, after we have sent the DATA without the FIN. We're waiting for that being ACKED on the OffsetCommit stream. For the PUBREL, we're just erasing the metadata on the offsetCommit for that packetId. That is the offsetCommitComplete. MQTT-Kafka binding is not sending the FIN bit as it closed the stream where the ACK should arrive on (offsetCommit).