SymmetricDispatcher has one kafka consumer, dispatcher can be launched into
multiple processes, kafka should auto balance its consumers therefore it is
symmetric.
validate required configuration zk.connect: zookeeper connection
metadata.broker.list: kafka broker list producer.topic: topic name this
producer sending to
Kafka only uses ZK in consumer config, the reason we expose this to
common configuration is we will optionally auto create the topic in
server kick off