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

tests/cloud_playbooks/roles/packet-ci/templates/inventory.j2

@@ -4,6 +4,10 @@ instance-{{ loop.index }} ansible_ssh_host={{instance.stdout}}
 {% endfor %}
 
 {% if mode is defined and mode in ["separate", "separate-scale"] %}
+[kube_control_plane]
+instance-1
+
+# TODO(oomichi): Remove all kube-master groups from this file after releasing v2.16.
 [kube-master]
 instance-1
 
@@ -13,6 +17,10 @@ instance-2
 [etcd]
 instance-3
 {% elif mode is defined and mode in ["ha", "ha-scale"] %}
+[kube_control_plane]
+instance-1
+instance-2
+
 [kube-master]
 instance-1
 instance-2
@@ -25,6 +33,9 @@ instance-1
 instance-2
 instance-3
 {% elif mode == "default" %}
+[kube_control_plane]
+instance-1
+
 [kube-master]
 instance-1
 
@@ -34,6 +45,9 @@ instance-2
 [etcd]
 instance-1
 {% elif mode == "aio" %}
+[kube_control_plane]
+instance-1
+
 [kube-master]
 instance-1
 
@@ -46,6 +60,10 @@ instance-1
 [vault]
 instance-1
 {% elif mode == "ha-recover" %}
+[kube_control_plane]
+instance-1
+instance-2
+
 [kube-master]
 instance-1
 instance-2
@@ -64,6 +82,11 @@ instance-2
 [broken_etcd]
 instance-2 etcd_member_name=etcd3
 {% elif mode == "ha-recover-noquorum" %}
+[kube_control_plane]
+instance-3
+instance-1
+instance-2
+
 [kube-master]
 instance-3
 instance-1