(TWILL-147) Allow using external Kafka server for log collection

[fonelor]

Now external kafka servers could be used for log aggregation Kafka updated to 0.10.2.0 Embedded kafka server starts if log aggregation is enabled and no external kafka servers configured removed old zk based kafka broker discovery service

[chtyim]

One quick question, does Kafka 0.10 client works with older version of Kafka server?

Also, ideally we should separate out all these Kafka related dependencies in a separate twill module, otherwise making it compatible with different Scala version would be quite difficult.