Merge pull request googleapis#2295 from dhermes/pubsub-sys-test-tweak

Correctly clean-up subscription in pubsub system test.

system_tests/pubsub.py

@@ -290,6 +290,7 @@ def _found_orphan(result):
                    if subscription.name == ORPHANED]
         self.assertEqual(len(created), 1)
         orphaned = created[0]
+        self.to_delete.append(orphaned)
 
         def _no_topic(instance):
             return instance.topic is None
@@ -298,4 +299,3 @@ def _no_topic(instance):
         retry_until_no_topic(orphaned.reload)()
 
         self.assertTrue(orphaned.topic is None)
-        orphaned.delete()