Now k8s cluster owner can do CA cert rotate to re-generate CA of
the cluster, service account keys and the certs of all nodes will
be regenerated as well. Cluster user needs to get a new kubeconfig
to access kubernetes API. This function is only supported by
Fedora CoreOS driver.
To test this patch with python-magnumclient, you need this patch
https://review.opendev.org/#/c/724243/, otherwise, you will see
an error about "not enough values to unpack", though the CA cert
rotate request has been processed by Magnum server side correctly.