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



Ok. So how about writing a Utils method that converts from one form to the other. As in String to list and vice versa. I mean currently there are two member variables in this class with the same info, just in different format. One is a list of brokers other is a String of a list of brokers. Don't you think it would be good to just have 1 member variable and util methods that can take you back and forth.