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-apps/ingress_controller/ambassador/tasks/main.yml

@@ -8,7 +8,7 @@
     group: root
     mode: 0755
   when:
-    - inventory_hostname == groups['kube-master'][0]
+    - inventory_hostname == groups['kube_control_plane'][0]
 
 - name: Ambassador | Templates list
   set_fact:
@@ -29,7 +29,7 @@
   loop: "{{ ingress_ambassador_templates }}"
   register: ingress_ambassador_manifests
   when:
-    - inventory_hostname == groups['kube-master'][0]
+    - inventory_hostname == groups['kube_control_plane'][0]
 
 - name: Ambassador | Apply manifests
   kube:
@@ -41,7 +41,7 @@
     state: "latest"
   loop: "{{ ingress_ambassador_manifests.results }}"
   when:
-    - inventory_hostname == groups['kube-master'][0]
+    - inventory_hostname == groups['kube_control_plane'][0]
 
 # load the AmbassadorInstallation _after_ the CustomResourceDefinition has been loaded
 
@@ -57,7 +57,7 @@
   loop: "{{ ingress_ambassador_cr_templates }}"
   register: ingress_ambassador_cr_manifests
   when:
-    - inventory_hostname == groups['kube-master'][0]
+    - inventory_hostname == groups['kube_control_plane'][0]
 
 - name: Ambassador | Apply AmbassadorInstallation
   kube:
@@ -69,4 +69,4 @@
     state: "latest"
   loop: "{{ ingress_ambassador_cr_manifests.results }}"
   when:
-    - inventory_hostname == groups['kube-master'][0]
+    - inventory_hostname == groups['kube_control_plane'][0]