Use init.d/gitlab script from 6-0-stable branch

Seems like init.d/gitlab script from master branch is not working anymore. Change to a version from 6-0-stable works fine.

It says:
```
Starting the GitLab Unicorn web server...
/etc/init.d/gitlab: 132: /etc/init.d/gitlab: script/web: not found
Starting the GitLab Sidekiq event dispatcher...
/etc/init.d/gitlab: 141: /etc/init.d/gitlab: script/background_jobs: not found
GitLab is not running.
```