Enabling working integration tests (#504)

Enabling tests that work without any further modification as an
incremental step to enabling all integration tests.

Enabling 22 / 64 tests.

The following tests do not work today:

- gcp_appengine_firewall_rule
- gcp_bigtable_instance
- gcp_cloudfunctions_cloud_function
- gcp_cloudtasks_queue
- gcp_compute_backend_service
- gcp_compute_external_vpn_gateway
- gcp_compute_forwarding_rule
- gcp_compute_instance
- gcp_compute_instance_group
- gcp_compute_instance_group_manager
- gcp_compute_instance_group_template
- gcp_compute_node_group
- gcp_compute_region_autoscaler
- gcp_compute_region_instance_group_manager
- gcp_compute_region_target_http_proxy
- gcp_compute_region_target_https_proxy
- gcp_compute_region_url_map
- gcp_compute_route
- gcp_compute_router
- gcp_compute_ssl_certificate
- gcp_compute_target_http_proxy
- gcp_compute_target_https_proxy
- gcp_compute_target_instance
- gcp_compute_target_pool
- gcp_compute_target_ssl_proxy
- gcp_compute_target_tcp_proxy
- gcp_compute_target_vpn_proxy
- gcp_container_cluster
- gcp_container_node_pool
- gcp_iam_role
- gcp_iam_service_account
- gcp_iam_service_account_key
- gcp_kms_key_ring
- gcp_mlengine_version
- gcp_redis_instance
- gcp_resourcemanager_project
- gcp_serviceusage_service
- gcp_spanner_database
- gcp_spanner_instance
- gcp_sql_ssl_cert
- gcp_storage_bucket
- gcp_tpu_node

CONTRIBUTING.md

@@ -40,6 +40,20 @@ gcp_cred_kind: @CRED_KIND
 gcp_cred_email: @EMAIL
 ```
 
+#### Setting up the project for testing
+
+Some of the setup of the project itself is done outside of the test,
+and is expected to be configured beforehand.
+
+For convenience, a bootstrap script is provided.
+
+NOTE: running this script will make irreversible changes in your
+GCP project (e.g. create an AppEngine project):
+
+```bash
+bash ./scripts/bootstrap-project.sh $PROJECT_ID $SERVICE_ACCOUNT_NAME
+```
+
 ### Running
 
 Run `ansible-test integration`. Currently some tests are disabled as [test are being verified and added](https://github.com/ansible-collections/google.cloud/issues/499).