The internal api returns '/' from gitlab, since
`8fad07383ada021fc995294fd0fe0f77fe37da35` from GitLab CE. To clean up
later, https://gitlab.com/gitlab-org/gitlab-shell/issues/135 was
created.

This change closes that issue, making it possible to remove the field
from the response on GitLab-CE too. Given the Rails app always returns
`/` as the repository_path, the associated checks are basically a noop
too. The tests are updated and at times look a little fishy, but those
are testing code that is to be removed in another MR.

Closes https://gitlab.com/gitlab-org/gitlab-shell/issues/135