Token infrastructure for running clients which are not kerberos authenticated

The JobClient.getDelegationToken() method is returning NULL, this makes Oozie fail when trying to get the delegation token to use it for starting a job.

What is seems to be happing is that Jobclient.getDelegationToken() calls Cluster.getDelegationToken() that calls YarnRunner.getDelegationToken() that calls ResourceMgrDelegate.getDelegationToken(). And the last one is not implemented. (Thanks Ahmed for tracing this in MR2 code)