COOPR-615: Enable kerberos login for zookeeper.

@jwang47 Added kerberos login to secure communications with ZooKeeper.

I have tested the fix locally and as result got next messages in ZooKeeper:
2014-12-18 18:39:33,649 [myid] - INFO  [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxnFactory@197] - Accepted socket connection from /127.0.0.1:52630
Found key for zookeeper/example.com@EXAMPLE.COM(23)
Found key for zookeeper/example.com@EXAMPLE.COM(16)
Found key for zookeeper/example.com@EXAMPLE.COM(1)
2014-12-18 18:39:33,651 [myid] - INFO  [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:ZooKeeperServer@868] - Client attempting to establish new session at /127.0.0.1:52630
2014-12-18 18:39:33,662 [myid] - INFO  [SyncThread:0:ZooKeeperServer@617] - Established session 0x14a5e3c7ff40001 with negotiated timeout 40000 for client /127.0.0.1:52630

The cdap-security will be replaced by common-security, when this refactoring will done.