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/templates/k8s-certs-renew.timer.j2

@@ -3,7 +3,7 @@ Description=Timer to renew K8S control plane certificates
 
 [Timer]
 # First Monday of each month
-OnCalendar=Mon *-*-1..7 03:{{ groups['kube-master'].index(inventory_hostname) }}0:00
+OnCalendar=Mon *-*-1..7 03:{{ groups['kube_control_plane'].index(inventory_hostname) }}0:00
 
 [Install]
 WantedBy=multi-user.target

roles/kubernetes/control-plane/templates/kubeadm-config.v1beta2.yaml.j2

@@ -16,7 +16,7 @@ nodeRegistration:
 {% if kube_override_hostname|default('') %}
   name: {{ kube_override_hostname }}
 {% endif %}
-{% if inventory_hostname in groups['kube-master'] and inventory_hostname not in groups['kube-node'] %}
+{% if inventory_hostname in groups['kube_control_plane'] and inventory_hostname not in groups['kube-node'] %}
   taints:
   - effect: NoSchedule
     key: node-role.kubernetes.io/master