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

extra_playbooks/migrate_openstack_provider.yml

@@ -1,5 +1,5 @@
 ---
-- hosts: kube-node:kube-master
+- hosts: kube-node:kube_control_plane
   tasks:
     - name: Remove old cloud provider config
       file:
@@ -7,7 +7,7 @@
         state: absent
       with_items:
         - /etc/kubernetes/cloud_config
-- hosts: kube-master[0]
+- hosts: kube_control_plane[0]
   tasks:
     - name: Include kubespray-default variables
       include_vars: ../roles/kubespray-defaults/defaults/main.yaml

extra_playbooks/upgrade-only-k8s.yml

@@ -34,7 +34,7 @@
     - { role: kubernetes/preinstall, tags: preinstall }
 
 - name: Handle upgrades to master components first to maintain backwards compat.
-  hosts: kube-master
+  hosts: kube_control_plane
   any_errors_fatal: "{{ any_errors_fatal | default(true) }}"
   serial: 1
   roles:
@@ -47,7 +47,7 @@
     - { role: upgrade/post-upgrade, tags: post-upgrade }
 
 - name: Finally handle worker upgrades, based on given batch size
-  hosts: kube-node:!kube-master
+  hosts: kube-node:!kube_control_plane
   any_errors_fatal: "{{ any_errors_fatal | default(true) }}"
   serial: "{{ serial | default('20%') }}"
   roles: