Workaround target pool issue by listing instances as zone/name

* Instances can be listed by zone/name or self_link URL, but the
provider desires they be in zone/name form, which causes a diff
* https://github.com/terraform-providers/terraform-provider-google/issues/46

google-cloud/container-linux/kubernetes/controllers/network.tf

@@ -30,7 +30,7 @@ resource "google_compute_target_pool" "controllers" {
   name = "${var.cluster_name}-controller-pool"
 
   instances = [
-    "${google_compute_instance.controllers.*.self_link}",
+    "${formatlist("%s/%s", google_compute_instance.controllers.*.zone, google_compute_instance.controllers.*.name)}"
   ]
 
   health_checks = [