Add exitCode to diagnostics when container fails

      String message = "Container completed. ";
      TaskAttemptTerminationCause errCause = TaskAttemptTerminationCause.CONTAINER_EXITED;
      int exitStatus = containerStatus.getExitStatus();
      if (exitStatus == ContainerExitStatus.PREEMPTED) {
        message = "Container preempted externally. ";
        errCause = TaskAttemptTerminationCause.EXTERNAL_PREEMPTION;
      } else if (exitStatus == ContainerExitStatus.DISKS_FAILED) {
        message = "Container disk failed. ";
        errCause = TaskAttemptTerminationCause.NODE_DISK_ERROR;
      } else if (exitStatus != ContainerExitStatus.SUCCESS){
        message = "Container failed. ";
      }
      if (containerStatus.getDiagnostics() != null) {
        message += containerStatus.getDiagnostics();
      }
      sendEvent(new AMContainerEventCompleted(amContainer.getContainerId(), exitStatus, message, errCause));