Stop using dockerfile/* images

As per
http://blog.docker.com/2015/03/updates-available-to-popular-repos-update-your-images/
docker has stopped answering dockerfile/redis and dockerfile/nginx.  Fix all
users in our tree.  Sadly this means a lot of published examples are now broken.

test/e2e/pods.go

@@ -483,7 +483,7 @@ var _ = Describe("Pods", func() {
 					Containers: []api.Container{
 						{
 							Name:  "nginx",
-							Image: "dockerfile/nginx",
+							Image: "nginx",
 						},
 					},
 				},
@@ -555,7 +555,7 @@ var _ = Describe("Pods", func() {
 					Containers: []api.Container{
 						{
 							Name:  "nginx",
-							Image: "dockerfile/nginx",
+							Image: "nginx",
 							Ports: []api.Port{{ContainerPort: 80}},
 						},
 					},