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-inventory/templates/inventory.j2

@@ -7,9 +7,9 @@
 {% endif %}
 {% endfor %}
 
-[kube-master]
+[kube_control_plane]
 {% for vm in vm_list %}
-{% if 'kube-master' in vm.tags.roles %}
+{% if 'kube_control_plane' in vm.tags.roles %}
 {{ vm.name }}
 {% endif %}
 {% endfor %}
@@ -30,4 +30,4 @@
 
 [k8s-cluster:children]
 kube-node
-kube-master
+kube_control_plane