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.

pkg/api/validation/testdata/v1beta3/invalidPod.yaml

@@ -7,5 +7,5 @@ metadata:
 spec:
   containers:
   - args: "this is a bad command"
-    image: dockerfile/redis
+    image: redis
     name: master

pkg/api/validation/testdata/v1beta3/invalidPod1.json

@@ -11,7 +11,7 @@
     "containers": [
       {
         "name": "master",
-        "image": "dockerfile/redis",
+        "image": "redis",
         "args": "this is a bad command"
       }
     ]

pkg/api/validation/testdata/v1beta3/validPod.yaml

@@ -12,5 +12,5 @@ spec:
     - an
     - ok
     - command
-    image: dockerfile/redis
+    image: redis
     name: master