Fix "google_compute_target_pool.workers: Cannot determine region"

If no region is set at the Google provider level, Terraform fails to
create the google_compute_target_pool.workers resource and complains
with "Cannot determine region: set in this resource, or set provider-level 'region' or 'zone'."

This commit fixes the issue by explicitly setting the region for the
google_compute_target_pool.workers resource.

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

@@ -1,6 +1,7 @@
 # Target pool for TCP/UDP load balancing
 resource "google_compute_target_pool" "workers" {
   name             = "${var.name}-worker-pool"
+  region           = "${var.region}"
   session_affinity = "NONE"
 
   health_checks = [