Switch to k8s.gcr.io vanity domain

This is the 2nd attempt.  The previous was reverted while we figured out
the regional mirrors (oops).

New plan: k8s.gcr.io is a read-only facade that auto-detects your source
region (us, eu, or asia for now) and pulls from the closest.  To publish
an image, push k8s-staging.gcr.io and it will be synced to the regionals
automatically (similar to today).  For now the staging is an alias to
gcr.io/google_containers (the legacy URL).

When we move off of google-owned projects (working on it), then we just
do a one-time sync, and change the google-internal config, and nobody
outside should notice.

We can, in parallel, change the auto-sync into a manual sync - send a PR
to "promote" something from staging, and a bot activates it.  Nice and
visible, easy to keep track of.

examples/volumes/portworx/portworx-volume-pod.yaml

@@ -4,7 +4,7 @@ metadata:
   name: test-portworx-volume-pod
 spec:
   containers:
-  - image: gcr.io/google_containers/test-webserver
+  - image: k8s.gcr.io/test-webserver
     name: test-container
     volumeMounts:
     - mountPath: /test-portworx-volume

examples/volumes/portworx/portworx-volume-pvcpod.yaml

@@ -5,7 +5,7 @@ metadata:
 spec:
   containers:
   - name: test-container
-    image: gcr.io/google_containers/test-webserver
+    image: k8s.gcr.io/test-webserver
     volumeMounts:
     - name: test-volume
       mountPath: /test-portworx-volume

examples/volumes/portworx/portworx-volume-pvcscpod.yaml

@@ -5,7 +5,7 @@ metadata:
 spec:
   containers:
   - name: test-container
-    image: gcr.io/google_containers/test-webserver
+    image: k8s.gcr.io/test-webserver
     volumeMounts:
     - name: test-volume
       mountPath: /test-portworx-volume

examples/volumes/scaleio/pod-sc-pvc.yaml

@@ -5,7 +5,7 @@ metadata:
 spec:
   containers:
     - name: pod-sio-small-container
-      image: gcr.io/google_containers/test-webserver
+      image: k8s.gcr.io/test-webserver
       volumeMounts:
       - mountPath: /test
         name: test-data

examples/volumes/scaleio/pod.yaml

@@ -4,7 +4,7 @@ metadata:
   name: pod-0
 spec:
   containers:
-  - image: gcr.io/google_containers/test-webserver
+  - image: k8s.gcr.io/test-webserver
     name: pod-0
     volumeMounts:
     - mountPath: /test-pd

examples/volumes/vsphere/simple-statefulset.yaml

@@ -27,7 +27,7 @@ spec:
     spec:
       containers:
       - name: nginx
-        image: gcr.io/google_containers/nginx-slim:0.8
+        image: k8s.gcr.io/nginx-slim:0.8
         ports:
         - containerPort: 80
           name: web

examples/volumes/vsphere/vsphere-volume-pod.yaml

@@ -4,7 +4,7 @@ metadata:
   name: test-vmdk
 spec:
   containers:
-  - image: gcr.io/google_containers/test-webserver
+  - image: k8s.gcr.io/test-webserver
     name: test-container
     volumeMounts:
     - mountPath: /test-vmdk

examples/volumes/vsphere/vsphere-volume-pvcpod.yaml

@@ -5,7 +5,7 @@ metadata:
 spec:
   containers:
   - name: test-container
-    image: gcr.io/google_containers/test-webserver
+    image: k8s.gcr.io/test-webserver
     volumeMounts:
     - name: test-volume
       mountPath: /test-vmdk

examples/volumes/vsphere/vsphere-volume-pvcscpod.yaml

@@ -5,7 +5,7 @@ metadata:
 spec:
   containers:
   - name: test-container
-    image: gcr.io/google_containers/test-webserver
+    image: k8s.gcr.io/test-webserver
     volumeMounts:
     - name: test-volume
       mountPath: /test-vmdk