Replace kube-master with kube_control_plane (#7256)

This replaces kube-master with kube_control_plane because of [1]:

  The Kubernetes project is moving away from wording that is
  considered offensive. A new working group WG Naming was created
  to track this work, and the word "master" was declared as offensive.
  A proposal was formalized for replacing the word "master" with
  "control plane". This means it should be removed from source code,
  documentation, and user-facing configuration from Kubernetes and
  its sub-projects.

NOTE: The reason why this changes it to kube_control_plane not
      kube-control-plane is for valid group names on ansible.

[1]: https://github.com/kubernetes/enhancements/blob/master/keps/sig-cluster-lifecycle/kubeadm/2067-rename-master-label-taint/README.md#motivation

roles/container-engine/kata-containers/molecule/default/molecule.yml

@@ -15,14 +15,14 @@ platforms:
     memory: 1024
     nested: true
     groups:
-      - kube-master
+      - kube_control_plane
   - name: ubuntu20
     box: generic/ubuntu2004
     cpus: 1
     memory: 1024
     nested: true
     groups:
-      - kube-master
+      - kube_control_plane
 provisioner:
   name: ansible
   env: