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/node-label/tasks/main.yml

@@ -9,7 +9,7 @@
   until: result.status == 200
   retries: 10
   delay: 6
-  when: inventory_hostname == groups['kube-master'][0]
+  when: inventory_hostname == groups['kube_control_plane'][0]
 
 - name: Set role node label to empty list
   set_fact:
@@ -42,6 +42,6 @@
   command: >-
       {{ bin_dir }}/kubectl label node {{ kube_override_hostname | default(inventory_hostname) }} {{ item }} --overwrite=true
   loop: "{{ role_node_labels + inventory_node_labels }}"
-  delegate_to: "{{ groups['kube-master'][0] }}"
+  delegate_to: "{{ groups['kube_control_plane'][0] }}"
   changed_when: false
 ...