Test with dockerized kafka/zookeeper

[dantswain]

This will open the door to a few things:

• Testing against multiple versions of kafka
• Ensuring a clean slate for every run of the tests - maybe eventually get rid of the randomized topic names
• Maybe getting rid of the duplicate test runs

[dantswain]

This is partly done - as of #181 Travis is running the tests with docker, as of #182 the README is recommending testing with docker.

I'd still like to get testing of non-ssl and the other kafka version servers.

[joshuawscott]

@dantswain As far as I can tell this is done?

[Argonus]

We've it in docker already.