Update gitolite

In GitLab 2.9.x there was a bug which can lead to bad consequences such as #1754 or #1709. That solves them. Also that steps related to users who wants to update gitolite v2 to v3.

1. Backup all repositories. Just copy /home/git/repositories/* elsewhere.

2. Install new gitolite. See https://github.com/gitlabhq/gitlabhq/blob/master/doc/install/installation.md

3. Copy repositories back.

4. Update gitolite config

sudo -u gitlab -H bundle exec rake gitlab:gitolite:update_keys RAILS_ENV=production
sudo -u gitlab -H bundle exec rake gitlab:gitolite:update_repos RAILS_ENV=production

5. Copy hooks

sudo cp ./lib/hooks/post-receive /home/git/.gitolite/hooks/common/post-receive
sudo chown git:git /home/git/.gitolite/hooks/common/post-receive

That's all.