Ensure all modules have an id output (#1410)

* net-vpc

* a-d

* complete modules

* fix error

modules/compute-mig/README.md

@@ -444,5 +444,6 @@ module "nginx-mig" {
 | [autoscaler](outputs.tf#L17) | Auto-created autoscaler resource. |  |
 | [group_manager](outputs.tf#L26) | Instance group resource. |  |
 | [health_check](outputs.tf#L35) | Auto-created health-check resource. |  |
+| [id](outputs.tf#L44) | Fully qualified group manager id. |  |
 
 <!-- END TFDOC -->

modules/compute-mig/outputs.tf

@@ -40,3 +40,12 @@ output "health_check" {
     : google_compute_health_check.default.0
   )
 }
+
+output "id" {
+  description = "Fully qualified group manager id."
+  value = try(
+    google_compute_instance_group_manager.default.0.id,
+    google_compute_region_instance_group_manager.default.0.id,
+    null
+  )
+}