Add self tests; use Odoo official repos

Highlights:
  - The `.travis.yml` is now capable to self test the quality tools.
  - Odoo installation now uses the official Odoo repo and pip installs dependencies.
  - Fixed a couple of issues revealed by the self tests.

Enjoy.
We're doing a different success check for <=7.0 and >=8.0. See @bwrsandman [comment](https://github.com/OCA/maintainer-quality-tools/pull/29#issuecomment-48826907) and the mentioned PR.