gitlab-rake gitlab:import:repos schedules an import

I've found the weird behaviour here: https://gitlab.com/gitlab-org/gitlab-ce/issues/41259#note_52131818

And @dbalexandre confirmed it.

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/15823 introduced another bug, meaning that being an import it schedules a new import on:

https://gitlab.com/gitlab-org/gitlab-ce/blob/master/app/services/projects/create_service.rb#L128