Add a label to prefix all container image use by magnum:
* kubernetes components
* coredns
* node-exporter
* kubernetes-dashboard
Using this label all containers will be pulled from the specified
registry and group in the registry.
TODO:
* grafana
* prometheus
Closes-Bug: #1712810
Change-Id: Iefe02f5ebc97787ee80431e0f16f73ae8444bdc0