Added TerminationGracePeriod field to PodSpec and grace-period flag to kubectl stop

Those are changes which touch users required by Termination Notice

Addresses #6804

pkg/kubelet/mirror_client.go

@@ -64,7 +64,7 @@ func (mc *basicMirrorClient) DeleteMirrorPod(podFullName string) error {
 		return err
 	}
 	glog.V(4).Infof("Deleting a mirror pod %q", podFullName)
-	if err := mc.apiserverClient.Pods(namespace).Delete(name); err != nil {
+	if err := mc.apiserverClient.Pods(namespace).Delete(name, nil); err != nil {
 		glog.Errorf("Failed deleting a mirror pod %q: %v", podFullName, err)
 	}
 	return nil