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/terraform/packet/kubespray.tf

@@ -19,7 +19,7 @@ resource "packet_device" "k8s_master" {
   operating_system = var.operating_system
   billing_cycle    = var.billing_cycle
   project_id       = var.packet_project_id
-  tags             = ["cluster-${var.cluster_name}", "k8s-cluster", "kube-master", "etcd", "kube-node"]
+  tags             = ["cluster-${var.cluster_name}", "k8s-cluster", "kube_control_plane", "etcd", "kube-node"]
 }
 
 resource "packet_device" "k8s_master_no_etcd" {
@@ -32,7 +32,7 @@ resource "packet_device" "k8s_master_no_etcd" {
   operating_system = var.operating_system
   billing_cycle    = var.billing_cycle
   project_id       = var.packet_project_id
-  tags             = ["cluster-${var.cluster_name}", "k8s-cluster", "kube-master"]
+  tags             = ["cluster-${var.cluster_name}", "k8s-cluster", "kube_control_plane"]
 }
 
 resource "packet_device" "k8s_etcd" {