[Sprint 39] [master] XD-2333 Add Kafka integration test

  - Add kafka test support class that checks for kafka server availablity on localhost
     - This uses zk server available on default connect string `localhost:2181`
  - Add test for verifying kafka source and sink
     - having both the source/sink on the same test case will make sure the topic that
gets the data by kafka sink is actually read by kafka source
Is just checking zookeeper enough? In the extension, I check both zk and kafka ports are listening...

https://github.com/spring-projects/spring-integration-kafka/blob/master/src/test/java/org/springframework/integration/kafka/rule/KafkaRunning.java#L66

Plus it's fast and doesn't produce log garbage when they are down.