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

contrib/azurerm/roles/generate-templates/templates/masters.json

@@ -144,7 +144,7 @@
         "[concat('Microsoft.Network/networkInterfaces/', 'master-{{i}}-nic')]"
       ],
       "tags": {
-        "roles": "kube-master,etcd"
+        "roles": "kube_control_plane,etcd"
       },
       "apiVersion": "{{apiVersion}}",
       "properties": {