Do not skip `rename_folder()` integration test

[coryan]

We use rename_folder() in the integration tests to verify LROs work correctly in the StorageControl client. It is relatively fast for new and empty folders (unlike most LROs).

However the function does not work with "custom billing projects". So the test is skipped if the default credentials use the x-goog-user-project header.

We can cleanup the tests when the service supports custom billing projects and then close this issue.