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/kubernetes/control-plane/tasks/encrypt-at-rest.yml

@@ -28,7 +28,7 @@
     kube_encrypt_token: "{{ kube_encrypt_token_extracted }}"
   delegate_to: "{{ item }}"
   delegate_facts: true
-  with_inventory_hostnames: kube-master
+  with_inventory_hostnames: kube_control_plane
   when: kube_encrypt_token_extracted is defined
 
 - name: Write secrets for encrypting secret data at rest