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/tokens/tasks/check-tokens.yml

@@ -5,7 +5,7 @@
     get_attributes: no
     get_checksum: yes
     get_mime: no
-  delegate_to: "{{ groups['kube-master'][0] }}"
+  delegate_to: "{{ groups['kube_control_plane'][0] }}"
   register: known_tokens_master
   run_once: true
 
@@ -32,7 +32,7 @@
   set_fact:
     sync_tokens: >-
       {%- set tokens = {'sync': False} -%}
-      {%- for server in groups['kube-master'] | intersect(ansible_play_batch)
+      {%- for server in groups['kube_control_plane'] | intersect(ansible_play_batch)
         if (not hostvars[server].known_tokens.stat.exists) or
         (hostvars[server].known_tokens.stat.checksum|default('') != known_tokens_master.stat.checksum|default('')) -%}
         {%- set _ = tokens.update({'sync': True}) -%}