operator: syncUpgrade should ignore notFound in Delete()

fix the issue that syncUpgrade will keep failing and not make any
progress.

pkg/operator/sync.go

@@ -294,7 +294,7 @@ func (v *Vaults) syncUpgrade(vr *api.VaultService, d *appsv1beta1.Deployment) (e
 		// If it failed for some reason, kubelet will send SIGKILL after default grace period (30s) eventually.
 		// It take longer but the the lock will get released eventually on failure case.
 		err = v.kubecli.CoreV1().Pods(vr.Namespace).Delete(vr.Status.ActiveNode, nil)
-		if err != nil {
+		if err != nil && !apierrors.IsNotFound(err) {
 			return fmt.Errorf("step down: failed to delete active Vault pod (%s): %v", vr.Status.ActiveNode, err)
 		}
 	}