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/remove-node/post-remove/tasks/main.yml

@@ -1,5 +1,5 @@
 ---
 - name: Delete node  # noqa 301
   command: "{{ bin_dir }}/kubectl delete node {{ kube_override_hostname|default(inventory_hostname) }}"
-  delegate_to: "{{ groups['kube-master']|first }}"
+  delegate_to: "{{ groups['kube_control_plane']|first }}"
   ignore_errors: yes