STORM-348: Netty SASL Authentication

Hi Bobby,
  I have made the changes for the SASL Netty Authentication.  Currently the credentials used is with the topology name, but I thought I would be using Kerberos token instead as we agreed I will use randomly generated credentials that are kept in zookeeper.  I will try to find it out which method to call or if you can help me out it would be great.  In the meantime you can review the changes.

 I have tested the changes but didn't create the unit tests.  I will create a separate JIRA for unit test and get it done.  I am learning Clojure and will get it done soon.

Thanks,
Raghavendra Nandagopal
Do we want to try and support the wrap/unwrap functionality in SASL?  I assume we don't need to at the beginning, but some people have asked for wire encryption and this could be an option.