kubectl describe: print toleration tolerating everything

An empty key with operator Exists matches all keys, values
and effects which means this will tolerate everything:
tolerations:
- operator: "Exists"

as stated in https://kubernetes.io/docs/concepts/scheduling-eviction/taint-and-toleration/.

However, the current printTolerationsMultilineWithIndent implementation ignores
this case. As the toleration is valid, there's no reason
to skip it when writing the list of all pod's tolerations.

staging/src/k8s.io/kubectl/pkg/describe/describe.go

@@ -4606,6 +4606,17 @@ func printTolerationsMultilineWithIndent(w PrefixWriter, initialIndent, title, i
 		if len(toleration.Effect) != 0 {
 			w.Write(LEVEL_0, ":%s", toleration.Effect)
 		}
+		// tolerations:
+		// - operator: "Exists"
+		// is a special case which tolerates everything
+		if toleration.Operator == corev1.TolerationOpExists && len(toleration.Value) == 0 {
+			if len(toleration.Key) != 0 {
+				w.Write(LEVEL_0, " op=Exists")
+			} else {
+				w.Write(LEVEL_0, "op=Exists")
+			}
+		}
+
 		if toleration.TolerationSeconds != nil {
 			w.Write(LEVEL_0, " for %ds", *toleration.TolerationSeconds)
 		}

staging/src/k8s.io/kubectl/pkg/describe/describe_test.go

@@ -179,6 +179,7 @@ func TestDescribePodTolerations(t *testing.T) {
 		},
 		Spec: corev1.PodSpec{
 			Tolerations: []corev1.Toleration{
+				{Operator: corev1.TolerationOpExists},
 				{Key: "key0", Operator: corev1.TolerationOpExists},
 				{Key: "key1", Value: "value1"},
 				{Key: "key2", Operator: corev1.TolerationOpEqual, Value: "value2", Effect: corev1.TaintEffectNoSchedule},
@@ -193,7 +194,8 @@ func TestDescribePodTolerations(t *testing.T) {
 	if err != nil {
 		t.Errorf("unexpected error: %v", err)
 	}
-	if !strings.Contains(out, "key0\n") ||
+	if !strings.Contains(out, "  op=Exists\n") ||
+		!strings.Contains(out, "key0 op=Exists\n") ||
 		!strings.Contains(out, "key1=value1\n") ||
 		!strings.Contains(out, "key2=value2:NoSchedule\n") ||
 		!strings.Contains(out, "key3=value3:NoExecute for 300s\n") ||