ability to support includes/excludes list in Hbase

This change adds support for includes and excludes list in HBase. To use it, specify the following properties in the hbase configuration file: hbase.hosts - for the includes file hbase.hosts.exclude - for the excludes file Both the files are optional. If the includes file is missing, any node is allowed (except the ones in the exclude file) If the includes file is present, then a node has to be present in the includes file and absent from the excludes file, to be able to successfully join. These files can be changed when the server is running. After changing these files, you can use the hbase console to issue 'refresh_nodes' command for the master to pick up the new config. If an online region server is added to the excludes file, 'refresh_nodes' will kick it out, with a specific exception. When the region server gets that exception, it shuts itself down.