11e7f330fb
Explain how to select a specific Kubernetes version by specifying the kube_tag label. In the process, also fix the broken list of images that must be mirrored, immediately above kube_tag. In addition, fix an unrelated whitespace error in specs/containers-service.rst which would cause tox -e docs to fail. Change-Id: Ieff1474b74e0b1595c05d945b69bec16bfef9c3b