[BUG FIX] Added a random hash key based on the event

Problem:
Having nil prevented kafka to send messages to different partitions. (nil will be of no use for the partition function, ie: kafka.producer.DefaultPartitioner) 

Zlib::crc32(event) uses 250ns aprox. and 'zlib' is part of the standard library, so no dependencies to load.

Reference:
http://programmers.stackexchange.com/questions/49550/which-hashing-algorithm-is-best-for-uniqueness-and-speed


This needs to be `@producer.sendMsg(@topic_id, "#{Zlib::crc32(event)}", event)` to avoid the error `kafka producer threw exception, restarting {:exception=>java.lang.ClassCastException: java.lang.Long cannot be cast to java.lang.String, :level=>:warn}`