Update GitLab software to

    - gitlab-ce 8.4 + NXD patches

      https://lab.nexedi.com/kirr/gitlab-ce/commits/8-4-nxd

    - gitlab-shell to 2.6.10 which now is pure upstream, as all NXD
      patches were merged.

    - gitlab-workhorse 0.6.X + NXD patches.

      https://lab.nexedi.com/kirr/gitlab-workhorse/commits/y/blobraw-3
      https://gitlab.com/gitlab-org/gitlab-workhorse/merge_requests/17

This only updates software and begins SR update to 8.4 - for now gitlab
instance becomes non-working -- we'll pull in configuration files
updates and fixups in the following patches.

/cc @kazuhiko, @jerome