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

Those are changes which touch users required by Termination Notice

Addresses #6804

test/e2e/networking.go

@@ -188,7 +188,7 @@ var _ = Describe("Networking", func() {
 			defer GinkgoRecover()
 			By("Cleaning up the webserver pods")
 			for _, podName := range podNames {
-				if err = c.Pods(namespace.Name).Delete(podName); err != nil {
+				if err = c.Pods(namespace.Name).Delete(podName, nil); err != nil {
 					Logf("Failed to delete pod %s: %v", podName, err)
 				}
 			}