Improvements to kafka_int_tests

[rukai]

We are seeing some issues with kafka in a test setup that are not showing up in our integration tests.
I've got a few ideas as to why it passes in our integration test but fails here:

• It could be specific to the java driver, we currently only test against the C/C++ driver.
• It could be specific to the way the cluster is setup. Currently we only test against against a cluster of 3 nodes without racks configured.

We should investigate adding the following to our test suite:

• 6 node cluster across 2 racks.
• Add the java driver as a backend to KafkaConnectionBuilder.

[rukai]

Both of these have been completed.