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-upgrade.yml

@@ -3,7 +3,7 @@
   uri:
     url: "https://{{ ip | default(fallback_ips[inventory_hostname]) }}:{{ kube_apiserver_port }}/healthz"
     validate_certs: false
-  when: inventory_hostname in groups['kube-master']
+  when: inventory_hostname in groups['kube_control_plane']
   register: _result
   retries: 60
   delay: 5
@@ -23,7 +23,7 @@
   # Retry is because upload config sometimes fails
   retries: 3
   until: kubeadm_upgrade.rc == 0
-  when: inventory_hostname == groups['kube-master']|first
+  when: inventory_hostname == groups['kube_control_plane']|first
   failed_when: kubeadm_upgrade.rc != 0 and "field is immutable" not in kubeadm_upgrade.stderr
   environment:
     PATH: "{{ bin_dir }}:{{ ansible_env.PATH }}"
@@ -40,7 +40,7 @@
     --etcd-upgrade={{ etcd_kubeadm_enabled | bool | lower }}
     --force
   register: kubeadm_upgrade
-  when: inventory_hostname != groups['kube-master']|first
+  when: inventory_hostname != groups['kube_control_plane']|first
   failed_when:
     - kubeadm_upgrade.rc != 0
     - '"field is immutable" not in kubeadm_upgrade.stderr'