This patch switches the kafka python client from kafka-python to
confluent-kafka due to documented threading issues with the
kafka-python consumer and the recommendation to use multiplrocessing.
The confluent-kafka client leverages the high performance librdkafka
C client and is safe for multiple thread use.
This patch:
* switches to confluent-kafka library
* revises consumer and producer message operations
* utilizes event.tpool method for confluent-kafka blocking calls
* updates unit tests
* adds kafka specific timeouts for functional tests
* adds release note
Depends-On: Ice374dca539b8ed1b1965b75379bad5140121483
Change-Id: Idfb9fe3700d882c8285c6dc56b0620951178eba2
5a842ae155