During the upgrade process, `kubeadm` will take the current
`ClusterConfiguration`, update the `KubernetesVersion` to the latest
version, and call to `UploadConfiguration`.

This change makes sure that when the mutation happens, not only the
`ClusterStatus` is mutated, but the `ClusterConfiguration` object
inside the `kubeadm-config` ConfigMap as well; it will contain the
new `KubernetesVersion`.