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

docs/calico.md

@@ -122,7 +122,7 @@ recommended here:
 You need to edit your inventory and add:
 
 * `calico-rr` group with nodes in it. `calico-rr` can be combined with
-  `kube-node` and/or `kube-master`. `calico-rr` group also must be a child
+  `kube-node` and/or `kube_control_plane`. `calico-rr` group also must be a child
    group of `k8s-cluster` group.
 * `cluster_id` by route reflector node/group (see details
 [here](https://hub.docker.com/r/calico/routereflector/))
@@ -138,7 +138,7 @@ node3 ansible_ssh_host=10.210.1.13 ip=10.210.1.13
 node4 ansible_ssh_host=10.210.1.14 ip=10.210.1.14
 node5 ansible_ssh_host=10.210.1.15 ip=10.210.1.15
 
-[kube-master]
+[kube_control_plane]
 node2
 node3
 
@@ -155,7 +155,7 @@ node5
 
 [k8s-cluster:children]
 kube-node
-kube-master
+kube_control_plane
 calico-rr
 
 [calico-rr]