Fix gitolite installation path in gitlab:env:info (based on b6568db1)

Created by: VonC

(related to #2480 (closed) and #2503 (closed))

This tasks presume of a fixed path for gitolite, relative to repos_path. info.rake uses "#{Gitlab.config.gitolite.repos_path}/../gitolite/src/VERSION"

However, you can install gitolite wherever you want. Hence this pathc:

M config/gitlab.yml.example: Add 'install_path' in 'gitolite' section M lib/tasks/gitlab/info.rake: Uses '"#{Gitlab.config.gitolite.install_path}