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.

cluster/addons/calico-policy-controller/calico-node-vertical-autoscaler-deployment.yaml

@@ -17,7 +17,7 @@ spec:
         scheduler.alpha.kubernetes.io/critical-pod: ''
     spec:
       containers:
-        - image: gcr.io/google_containers/cpvpa-amd64:v0.6.0
+        - image: k8s.gcr.io/cpvpa-amd64:v0.6.0
           name: autoscaler
           command:
             - /cpvpa

cluster/addons/calico-policy-controller/typha-horizontal-autoscaler-deployment.yaml

@@ -17,7 +17,7 @@ spec:
         scheduler.alpha.kubernetes.io/critical-pod: ''
     spec:
       containers:
-        - image: gcr.io/google_containers/cluster-proportional-autoscaler-amd64:1.1.2
+        - image: k8s.gcr.io/cluster-proportional-autoscaler-amd64:1.1.2
           name: autoscaler
           command:
             - /cluster-proportional-autoscaler

cluster/addons/calico-policy-controller/typha-vertical-autoscaler-deployment.yaml

@@ -17,7 +17,7 @@ spec:
         scheduler.alpha.kubernetes.io/critical-pod: ''
     spec:
       containers:
-        - image: gcr.io/google_containers/cpvpa-amd64:v0.6.0
+        - image: k8s.gcr.io/cpvpa-amd64:v0.6.0
           name: autoscaler
           command:
             - /cpvpa