Acceptance testing was done in:
https://gitlab.com/gitlab-org/gitaly/issues/1146. Errors were limited to
NotFound errors, as the repository really doesn't exists.

Closes https://gitlab.com/gitlab-org/gitaly/issues/1146

Optimistically moved https://gitlab.com/gitlab-org/gitaly/issues/1105 to
opt out on the Gitaly migration board.