- git-clone and build git-backup sources
  - add a crontab doing `gitlab-backup pull` every 4 hours
  - add xnice for using less resources while backuping
  - add lock to avoid concurrent calls of backup script

Update GitLab software to

    - gitlab-ce 8.8.9 + NXD patches

    - gitlab-shell stays at 2.7.2 + 1 patch to remove unneeded hooks.old in *.git
      because gitlab-ce 8.7.x sticks to this version (i.e. no shell upgrade for
      gitlab 8.7 -> 8.8)

    - gitlab-workhorse stays at 0.7.1 + NXD patches because gitlab-ce 8.8.x
      sticks to this version (i.e. no workhorse upgrade for gitlab 8.7 -> 8.8)

This only updates software and begins SR update to 8.8 - for now gitlab
instance starts using gitlab-ce appropriate version.

it is no longer possible to use http:/ as curl now expect a hostname to be
given, see curl issue https://github.com/curl/curl/issues/936

Like for af0c5b11

    $ git diff 8-7-stable 8-8-stable --
            files/gitlab-cookbooks/gitlab/templates/default/sv-sidekiq-run.erb

is empty.

Like for 61177775.

I've manually reviewed

    git diff 8-7-stable 8-8-stable -- files/gitlab-config-template/gitlab.rb.template \
                                      files/gitlab-cookbooks/gitlab/attributes/default.rb

on omnibus-gitlab repository.

There are only changes on postgresql and registry options, which are not relevant for us.

Do not use container_registry and registry_* options

This does almost(*) only pure merge. We will slaposify / adjust config
and corresponding md5sum in the following patches.

(*) condition on smtp_authentication was applied by hand on smtp_settings.rb.in

In the case of hellorina SR, the following section generated invalid command:

[proxy]
command-line = {{ python_location }}/bin/python2.7 {{ rina_proxy }} ${server:instance-guid} ${:ipv6} ${:port}
...

This value can be used as a unique identifier within the cloud.
It was already available for the requesting partition ('request' recipe).

/reviewed-on nexedi/slapos!101