Fix overly strict firewall for GCP "worker pools"

* Fix issue where worker firewall rules didn't apply to
additional workers attached to a GCP cluster using the new
"worker pools" feature (unreleased, #148). Solves host
connection timeouts and pods not being scheduled to attached
worker pools.
* Add `name` field to GCP internal worker module to represent
the unique name of of the worker pool
* Use `cluster_name` field of GCP internal worker module for
passing the name of the cluster to which workers should be
attached

google-cloud/container-linux/kubernetes/workers/variables.tf

@@ -1,11 +1,16 @@
-variable "cluster_name" {
+variable "name" {
   type        = "string"
-  description = "Unique cluster name"
+  description = "Unique name"
 }
 
-variable "ssh_authorized_key" {
+variable "cluster_name" {
   type        = "string"
-  description = "SSH public key for logging in as user 'core'"
+  description = "Cluster name"
+}
+
+variable "region" {
+  type        = "string"
+  description = "Google Cloud region (e.g. us-central1, see `gcloud compute regions list`)."
 }
 
 variable "network" {
@@ -21,11 +26,6 @@ variable "count" {
   description = "Number of worker compute instances the instance group should manage"
 }
 
-variable "region" {
-  type        = "string"
-  description = "Google Cloud region (e.g. us-central1, see `gcloud compute regions list`)."
-}
-
 variable "machine_type" {
   type        = "string"
   default     = "n1-standard-1"
@@ -52,6 +52,16 @@ variable "preemptible" {
 
 # configuration
 
+variable "kubeconfig" {
+  type        = "string"
+  description = "Generated Kubelet kubeconfig"
+}
+
+variable "ssh_authorized_key" {
+  type        = "string"
+  description = "SSH public key for logging in as user 'core'"
+}
+
 variable "service_cidr" {
   description = <<EOD
 CIDR IP range to assign Kubernetes services.
@@ -67,8 +77,3 @@ variable "cluster_domain_suffix" {
   type        = "string"
   default     = "cluster.local"
 }
-
-variable "kubeconfig" {
-  type        = "string"
-  description = "Generated Kubelet kubeconfig"
-}