TestRecoveryManager fails sometimes

JobTracker was changed to take an identifier as an argument. This helps in testcases where the jobtracker/mapred-cluster is (re)started in a short span of time and the chances of jobtracker identifier clashing are high. Also the RecoveryManager was modified to throw an exception if a job fails in init during the recovery process. The reason being that this event will trigger a job failure in the recovery process and will remove the failed job from further initialization and processing.