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/fluentd-gcp/event-exporter.yaml

@@ -47,12 +47,12 @@ spec:
       serviceAccountName: event-exporter-sa
       containers:
       - name: event-exporter
-        image: gcr.io/google-containers/event-exporter:v0.1.7
+        image: k8s.gcr.io/event-exporter:v0.1.7
         command:
         - '/event-exporter'
       # BEGIN_PROMETHEUS_TO_SD
       - name: prometheus-to-sd-exporter
-        image: gcr.io/google-containers/prometheus-to-sd:v0.2.2
+        image: k8s.gcr.io/prometheus-to-sd:v0.2.2
         command:
           - /monitor
           - --stackdriver-prefix={{ prometheus_to_sd_prefix }}/addons

cluster/addons/fluentd-gcp/fluentd-gcp-ds.yaml

@@ -27,7 +27,7 @@ spec:
       dnsPolicy: Default
       containers:
       - name: fluentd-gcp
-        image: gcr.io/google-containers/fluentd-gcp:2.0.14
+        image: k8s.gcr.io/fluentd-gcp:2.0.14
         env:
         - name: FLUENTD_ARGS
           value: --no-supervisor -q
@@ -82,7 +82,7 @@ spec:
               fi;
       # BEGIN_PROMETHEUS_TO_SD
       - name: prometheus-to-sd-exporter
-        image: gcr.io/google-containers/prometheus-to-sd:v0.2.2
+        image: k8s.gcr.io/prometheus-to-sd:v0.2.2
         command:
           - /monitor
           - --stackdriver-prefix={{ prometheus_to_sd_prefix }}/addons