Fix resource leaks in xds test (#26967)

* allow clean up of leaked cb backend services

* auto-delete disk

* yapf

tools/run_tests/run_xds_tests.py

@@ -2422,7 +2422,8 @@ def create_instance_template(gcp, name, network, source_image, machine_type,
                 'boot': True,
                 'initializeParams': {
                     'sourceImage': source_image
-                }
+                },
+                'autoDelete': True
             }],
             'metadata': {
                 'items': [{
@@ -2649,12 +2650,13 @@ def get_health_check_firewall_rule(gcp, firewall_name):
         gcp.health_check_firewall_rule = GcpResource(firewall_name, None)
 
 
-def get_backend_service(gcp, backend_service_name):
+def get_backend_service(gcp, backend_service_name, record_error=True):
     try:
         result = gcp.compute.backendServices().get(
             project=gcp.project, backendService=backend_service_name).execute()
         backend_service = GcpResource(backend_service_name, result['selfLink'])
     except Exception as e:
+        if record_error:
             gcp.errors.append(e)
         backend_service = GcpResource(backend_service_name, None)
     gcp.backend_services.append(backend_service)
@@ -3132,6 +3134,8 @@ try:
     firewall_name = _BASE_FIREWALL_RULE_NAME + gcp_suffix
     backend_service_name = _BASE_BACKEND_SERVICE_NAME + gcp_suffix
     alternate_backend_service_name = _BASE_BACKEND_SERVICE_NAME + '-alternate' + gcp_suffix
+    extra_backend_service_name = _BASE_BACKEND_SERVICE_NAME + '-extra' + gcp_suffix
+    more_extra_backend_service_name = _BASE_BACKEND_SERVICE_NAME + '-more-extra' + gcp_suffix
     url_map_name = _BASE_URL_MAP_NAME + gcp_suffix
     service_host_name = _BASE_SERVICE_HOST + gcp_suffix
     target_proxy_name = _BASE_TARGET_PROXY_NAME + gcp_suffix
@@ -3149,6 +3153,11 @@ try:
         backend_service = get_backend_service(gcp, backend_service_name)
         alternate_backend_service = get_backend_service(
             gcp, alternate_backend_service_name)
+        extra_backend_service = get_backend_service(gcp,
+                                                    extra_backend_service_name,
+                                                    record_error=False)
+        more_extra_backend_service = get_backend_service(
+            gcp, more_extra_backend_service_name, record_error=False)
         get_url_map(gcp, url_map_name)
         get_target_proxy(gcp, target_proxy_name)
         get_global_forwarding_rule(gcp, forwarding_rule_name)