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/preinstall/tasks/0020-verify-settings.yml

@@ -1,9 +1,9 @@
 ---
-- name: Stop if either kube-master or kube-node group is empty
+- name: Stop if either kube_control_plane or kube-node group is empty
   assert:
     that: "groups.get('{{ item }}')"
   with_items:
-    - kube-master
+    - kube_control_plane
     - kube-node
   run_once: true
   when: not ignore_assert_errors
@@ -79,7 +79,7 @@
     that: ansible_memtotal_mb >= minimal_master_memory_mb
   when:
     - not ignore_assert_errors
-    - inventory_hostname in groups['kube-master']
+    - inventory_hostname in groups['kube_control_plane']
 
 - name: Stop if memory is too small for nodes
   assert:
@@ -136,7 +136,7 @@
   assert:
     that: rbac_enabled and kube_api_anonymous_auth
   when:
-    - kube_apiserver_insecure_port == 0 and inventory_hostname in groups['kube-master']
+    - kube_apiserver_insecure_port == 0 and inventory_hostname in groups['kube_control_plane']
     - not ignore_assert_errors
 
 - name: Stop if kernel version is too low
@@ -193,7 +193,7 @@
     - kube_network_plugin == 'calico'
     - 'calico_version_on_server.stdout is defined'
     - calico_version_on_server.stdout
-    - inventory_hostname == groups['kube-master'][0]
+    - inventory_hostname == groups['kube_control_plane'][0]
   run_once: yes
 
 - name: "Check that cluster_id is set if calico_rr enabled"
@@ -204,7 +204,7 @@
   when:
     - kube_network_plugin == 'calico'
     - peer_with_calico_rr
-    - inventory_hostname == groups['kube-master'][0]
+    - inventory_hostname == groups['kube_control_plane'][0]
   run_once: yes
 
 - name: "Check that calico_rr nodes are in k8s-cluster group"