Integrate testing

Reminder:
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* [x] Rspec test not fully fonctionnal (default task, thanks Steffen)
* [x] Bump to gitlab 4.1 (thanks Uwe)
* [ ] Use github API for tarball install (instead of GIT), see puppet-gitlab@bdeda158c44704e62750d83c980c051c3f04c968
* [x] Tested