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
The createSaslClient() method throws IOException and we just log it and make the saslClient object null which will end up with NPEs.  Is there anything that we need to take care?