Fix tab completion tests to work with S3.
Fix tab completion tests to work with S3.

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