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/node/tasks/install.yml

@@ -8,7 +8,7 @@
   tags:
     - kubeadm
   when:
-    - not inventory_hostname in groups['kube-master']
+    - not inventory_hostname in groups['kube_control_plane']
 
 - name: install | Copy kubelet binary from download dir
   copy:

roles/kubernetes/node/templates/loadbalancer/haproxy.cfg.j2

@@ -38,6 +38,6 @@ backend kube_api_backend
   default-server inter 15s downinter 15s rise 2 fall 2 slowstart 60s maxconn 1000 maxqueue 256 weight 100
   option httpchk GET /healthz
   http-check expect status 200
-  {% for host in groups['kube-master'] -%}
+  {% for host in groups['kube_control_plane'] -%}
   server {{ host }} {{ hostvars[host]['access_ip'] | default(hostvars[host]['ip'] | default(fallback_ips[host])) }}:{{ kube_apiserver_port }} check check-ssl verify none
   {% endfor -%}

roles/kubernetes/node/templates/loadbalancer/nginx.conf.j2

@@ -13,7 +13,7 @@ events {
 stream {
   upstream kube_apiserver {
     least_conn;
-    {% for host in groups['kube-master'] -%}
+    {% for host in groups['kube_control_plane'] -%}
     server {{ hostvars[host]['access_ip'] | default(hostvars[host]['ip'] | default(fallback_ips[host])) }}:{{ kube_apiserver_port }};
     {% endfor -%}
   }