RM should always be able to renew its own tokens

YARN-280 introduced fast-fail for job submissions with bad tokens. Unfortunately, other stack components like oozie and customers are acquiring RM tokens with a hardcoded dummy renewer value. These jobs would fail after 24 hours because the RM token couldn't be renewed, but fast-fail is failing them immediately. The RM should always be able to renew its own tokens submitted with a job. The renewer field may continue to specify an external user who can renew.