Port the downward api test to the node e2e suite

Also extend the framework to allow a custom client config loading function, so
that the node e2e suite can reuse the same framework across tests.

test/e2e_node/privileged_test.go

@@ -197,10 +197,6 @@ func waitForPodRunning(c *client.Client, ns string, name string) error {
 	return fmt.Errorf("Time out while waiting for pod %s/%s to become running; current status: %+v", ns, name, pod.Status)
 }
 
-func setNodeNameForPod(pod *api.Pod) {
-	pod.Spec.NodeName = *nodeName
-}
-
 func createPodAndWaitUntilRunning(c *client.Client, pod *api.Pod) *api.Pod {
 	ref := fmt.Sprintf("%v/%v", pod.Namespace, pod.Name)
 	_, err := createPodWithSpec(c, pod)
@@ -215,8 +211,7 @@ func createPodAndWaitUntilRunning(c *client.Client, pod *api.Pod) *api.Pod {
 func createPodWithSpec(c *client.Client, pod *api.Pod) (*api.Pod, error) {
 	// Manually assign pod to node because we don't run the scheduler in node
 	// e2e tests.
-	// TODO: This should also be a shared utility function.
-	setNodeNameForPod(pod)
+	assignPodToNode(pod)
 	createdPod, err := c.Pods(pod.Namespace).Create(pod)
 	return createdPod, err
 }