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/control-plane/tasks/kubeadm-secondary.yml

@@ -18,15 +18,15 @@
     --upload-certs
   register: kubeadm_upload_cert
   when:
-    - inventory_hostname == groups['kube-master']|first
+    - inventory_hostname == groups['kube_control_plane']|first
 
 - name: Parse certificate key if not set
   set_fact:
-    kubeadm_certificate_key: "{{ hostvars[groups['kube-master'][0]]['kubeadm_upload_cert'].stdout_lines[-1] | trim }}"
+    kubeadm_certificate_key: "{{ hostvars[groups['kube_control_plane'][0]]['kubeadm_upload_cert'].stdout_lines[-1] | trim }}"
   run_once: yes
   when:
-    - hostvars[groups['kube-master'][0]]['kubeadm_upload_cert'] is defined
-    - hostvars[groups['kube-master'][0]]['kubeadm_upload_cert'] is not skipped
+    - hostvars[groups['kube_control_plane'][0]]['kubeadm_upload_cert'] is defined
+    - hostvars[groups['kube_control_plane'][0]]['kubeadm_upload_cert'] is not skipped
 
 - name: Create kubeadm ControlPlane config
   template:
@@ -35,7 +35,7 @@
     mode: 0640
     backup: yes
   when:
-    - inventory_hostname != groups['kube-master']|first
+    - inventory_hostname != groups['kube_control_plane']|first
     - not kubeadm_already_run.stat.exists
 
 - name: Wait for k8s apiserver
@@ -64,5 +64,5 @@
   throttle: 1
   until: kubeadm_join_control_plane is succeeded
   when:
-    - inventory_hostname != groups['kube-master']|first
+    - inventory_hostname != groups['kube_control_plane']|first
     - kubeadm_already_run is not defined or not kubeadm_already_run.stat.exists