Add an extra place to look for the mock_storage_service.
Add an extra place to look for the mock_storage_service.

GoogleCloudPlatform/gsutil,dimfeld/gsutil,craigcitro/gsutil,BrandonY/gsutil,fishjord/gsutil,GoogleCloudPlatform/gsutil,chriskuehl/gsutil-debian,dtjackson/gsutil,ttiurani/gsutil,mattdr/gsutil