Prepare for content-type negotiation

Combine the fields that will be used for content transformation
(content-type, codec, and group version) into a single struct in client,
and then pass that struct into the rest client and request. Set the
content-type when sending requests to the server, and accept the content
type as primary.

Will form the foundation for content-negotiation via the client.

pkg/controller/controller_utils_test.go

@@ -192,7 +192,7 @@ func TestCreatePods(t *testing.T) {
 	testServer := httptest.NewServer(&fakeHandler)
 	// TODO: Uncomment when fix #19254
 	// defer testServer.Close()
-	client := client.NewOrDie(&client.Config{Host: testServer.URL, GroupVersion: testapi.Default.GroupVersion()})
+	client := client.NewOrDie(&client.Config{Host: testServer.URL, ContentConfig: client.ContentConfig{GroupVersion: testapi.Default.GroupVersion()}})
 
 	podControl := RealPodControl{
 		KubeClient: client,
@@ -212,7 +212,7 @@ func TestCreatePods(t *testing.T) {
 		Spec: controllerSpec.Spec.Template.Spec,
 	}
 	fakeHandler.ValidateRequest(t, testapi.Default.ResourcePath("pods", api.NamespaceDefault, ""), "POST", nil)
-	actualPod, err := runtime.Decode(client.Codec, []byte(fakeHandler.RequestBody))
+	actualPod, err := runtime.Decode(testapi.Default.Codec(), []byte(fakeHandler.RequestBody))
 	if err != nil {
 		t.Errorf("Unexpected error: %#v", err)
 	}