**What this PR does / why we need it**:

Remove kubectl's dependence on pkg/api/helper, as part of
broader effort to isolate kubectl from the rest of k8s.
In this case, the code becomes private to kubectl; nobody else uses it.

**Which issue this PR fixes**

Part of a series of PRs to address kubernetes/community#598

**Special notes for your reviewer**:

**Release note**:
```release-note
NONE
```

pkg/kubectl/util/util.go

@@ -0,0 +1,46 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package util
+
+import (
+	"crypto/md5"
+	"fmt"
+	"time"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime"
+)
+
+// ParseRFC3339 parses an RFC3339 date in either RFC3339Nano or RFC3339 format.
+func ParseRFC3339(s string, nowFn func() metav1.Time) (metav1.Time, error) {
+	if t, timeErr := time.Parse(time.RFC3339Nano, s); timeErr == nil {
+		return metav1.Time{Time: t}, nil
+	}
+	t, err := time.Parse(time.RFC3339, s)
+	if err != nil {
+		return metav1.Time{}, err
+	}
+	return metav1.Time{Time: t}, nil
+}
+
+func HashObject(obj runtime.Object, codec runtime.Codec) (string, error) {
+	data, err := runtime.Encode(codec, obj)
+	if err != nil {
+		return "", err
+	}
+	return fmt.Sprintf("%x", md5.Sum(data)), nil
+}