Use a lower-privilege Kubelet kubeconfig in system:nodes

* Kubelets can use a lower-privilege TLS client certificate with
Org system:nodes and a binding to the system:node ClusterRole
* Admin kubeconfig's continue to belong to Org system:masters to
provide cluster-admin (available in assets/auth/kubeconfig or as
a Terraform output kubeconfig-admin)
* Remove bare-metal output variable kubeconfig

aws/container-linux/kubernetes/bootkube.tf

@@ -1,6 +1,6 @@
 # Self-hosted Kubernetes assets (kubeconfig, manifests)
 module "bootkube" {
-  source = "git::https://github.com/poseidon/terraform-render-bootkube.git?ref=f382415f2bc18c7a2d39a92fe254e3823a634270"
+  source = "git::https://github.com/poseidon/terraform-render-bootkube.git?ref=a7bd306679a0ce8a9e5084f928af696a284a256b"
 
   cluster_name          = "${var.cluster_name}"
   api_servers           = ["${format("%s.%s", var.cluster_name, var.dns_zone)}"]

aws/container-linux/kubernetes/controllers.tf

@@ -68,7 +68,7 @@ data "template_file" "controller-configs" {
     # etcd0=https://cluster-etcd0.example.com,etcd1=https://cluster-etcd1.example.com,...
     etcd_initial_cluster = "${join(",", data.template_file.etcds.*.rendered)}"
 
-    kubeconfig            = "${indent(10, module.bootkube.kubeconfig)}"
+    kubeconfig            = "${indent(10, module.bootkube.kubeconfig-kubelet)}"
     ssh_authorized_key    = "${var.ssh_authorized_key}"
     k8s_dns_service_ip    = "${cidrhost(var.service_cidr, 10)}"
     cluster_domain_suffix = "${var.cluster_domain_suffix}"

aws/container-linux/kubernetes/outputs.tf

@@ -1,5 +1,5 @@
 output "kubeconfig-admin" {
-  value = "${module.bootkube.user-kubeconfig}"
+  value = "${module.bootkube.kubeconfig-admin-context}"
 }
 
 # Outputs for Kubernetes Ingress
@@ -27,7 +27,7 @@ output "worker_security_groups" {
 }
 
 output "kubeconfig" {
-  value = "${module.bootkube.kubeconfig}"
+  value = "${module.bootkube.kubeconfig-kubelet}"
 }
 
 # Outputs for custom load balancing

aws/container-linux/kubernetes/workers.tf

@@ -13,7 +13,7 @@ module "workers" {
   spot_price      = "${var.worker_price}"
 
   # configuration
-  kubeconfig            = "${module.bootkube.kubeconfig}"
+  kubeconfig            = "${module.bootkube.kubeconfig-kubelet}"
   ssh_authorized_key    = "${var.ssh_authorized_key}"
   service_cidr          = "${var.service_cidr}"
   cluster_domain_suffix = "${var.cluster_domain_suffix}"