Lorry1 can't mirror git-lfs repositories, add test to validate lorry2

Mirroring repositories that use git lfs fails with lorry 1

For instance, we have https://github.com/unicode-org/icu. Mirroring it fails with the following error message:

    remote: GitLab: LFS objects are missing. Ensure LFS is properly set up or try a manual "git lfs push --all".

Lorry 2 issue: lorry2#72 (closed)