Reduce NN calls in RecoveryService::handleRecoveryEvent

https://github.com/apache/tez/blob/master/tez-dag/src/main/java/org/apache/tez/dag/history/recovery/RecoveryService.java#L459

https://github.com/apache/tez/blob/master/tez-dag/src/main/java/org/apache/tez/dag/history/recovery/RecoveryService.java#L467

create(overwrite=false) already checks for file exists and throws relevant exception. It should be possible to reduce recoveryDirFS.exists(dagFilePath) check to help in concurrent job runs (e.g 50-100 AM trying to run very short jobs).