This PR adds the code for enabling gvisor in minikube. It adds the pod
that will run when the addon is enabled, and the code for the image
which will run when this happens.
When gvisor is enabled, the pod will download runsc and the
gvisor-containerd-shim. It will replace the containerd config.toml and
restart containerd.
When gvisor is disabled, the pod will be deleted by the addon manager.
This will trigger a pre-stop hook which will revert the config.toml to
it's original state and restart containerd.
Previously we were mixed between the two forms. This commit picks %v,
which is consistent with the Kubernetes code base. They both effectively
do the same thing in this case, though %v works with any object, and %s
only with string objects.