End-to-end tests for terraform modules (#1751)

Add end-to-end tests (apply, plan, destroy) for examples.

When run, `tests/examples_e2e`:
1. Create an environment for tests to run (folder, project vpc network) 
2. For each marked example (with `e2e` tftest directive), run apply, plan, destroy
3. Verify:
* no failure in apply
* empty plan after apply
* no failure during destroy
4. When all tests are done, destroy test environment

More details in `tests/examples_e2e/README.md`

modules/cloud-run/README.md

@@ -28,7 +28,7 @@ IAM bindings support the usual syntax. Container environment values can be decla
 ```hcl
 module "cloud_run" {
   source     = "./fabric/modules/cloud-run"
-  project_id = "my-project"
+  project_id = var.project_id
   name       = "hello"
   containers = {
     hello = {
@@ -49,7 +49,7 @@ module "cloud_run" {
     "roles/run.invoker" = ["allUsers"]
   }
 }
-# tftest modules=1 resources=2 inventory=simple.yaml
+# tftest modules=1 resources=2 inventory=simple.yaml e2e
 ```
 
 ### Mounting secrets as volumes