code: func isRollbackEvent(e *api.Event) (bool, string) {
  	rollbackEventReasons := []string{deploymentutil.RollbackRevisionNotFound, deploymentutil.RollbackTemplateUnchanged, deploymentutil.RollbackDone}
  	for _, reason := range rollbackEventReasons {
  		if e.Reason == reason {
  			if reason == deploymentutil.RollbackDone {
  				return true, "rolled back"
  			}
  			return true, fmt.Sprintf("skipped rollback (%s: %s)", e.Reason, e.Message)
  		}
  	}
  	return false, ""
  }
docs: // isRollbackEvent checks if the input event is about rollback, and returns true and
  // related result string back if it is.