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-apps/external_cloud_controller/openstack/tasks/main.yml

@@ -20,14 +20,14 @@
     dest: "{{ kube_config_dir }}/external_openstack_cloud_config"
     group: "{{ kube_cert_group }}"
     mode: 0640
-  when: inventory_hostname == groups['kube-master'][0]
+  when: inventory_hostname == groups['kube_control_plane'][0]
   tags: external-openstack
 
 - name: External OpenStack Cloud Controller | Get base64 cloud-config
   slurp:
     src: "{{ kube_config_dir }}/external_openstack_cloud_config"
   register: external_openstack_cloud_config_secret
-  when: inventory_hostname == groups['kube-master'][0]
+  when: inventory_hostname == groups['kube_control_plane'][0]
   tags: external-openstack
 
 - name: External OpenStack Cloud Controller | Generate Manifests
@@ -42,7 +42,7 @@
     - {name: external-openstack-cloud-controller-manager-role-bindings, file: external-openstack-cloud-controller-manager-role-bindings.yml}
     - {name: external-openstack-cloud-controller-manager-ds, file: external-openstack-cloud-controller-manager-ds.yml}
   register: external_openstack_manifests
-  when: inventory_hostname == groups['kube-master'][0]
+  when: inventory_hostname == groups['kube_control_plane'][0]
   tags: external-openstack
 
 - name: External OpenStack Cloud Controller | Apply Manifests
@@ -53,7 +53,7 @@
   with_items:
     - "{{ external_openstack_manifests.results }}"
   when:
-    - inventory_hostname == groups['kube-master'][0]
+    - inventory_hostname == groups['kube_control_plane'][0]
     - not item is skipped
   loop_control:
     label: "{{ item.item.file }}"