STORM-444 Adding AutoHBase Nimbus plugin.

sorry about not finishing this with STORM-346, Pulled some of the AutoHDFS code to a parent abstract class as both Hbase and HDFS leverages hadoop's UserGroupInformation, Credentials and Token classes. I have not been able to successfully verify AutoHbase on my local desktop as I am failing to setup secure HBase, Posting the pull request so I can start getting the feedback.