Hardening Kafka integration to Venice

Two key changes here:
- Allow Venice Consumer task to listen to multiple brokers and integrate with Kafka broker replication
- Provide kafka-broker-list to stores metadata, such that clients can produce to the correct topics



I was having problems where underlying methods were throwing exceptions that were not VoldemortVeniceException, and they would skip to the finally-block undetected.

My reasoning here is that if there is an uncaught exception, the task should be killed. (I have catch statements that will trigger leader re-election, so that will not end up here)