Update to librarian

Follow the `foreman-installer` and use `librarian` to manage the dependent puppet modules.

However, unlike in `foreman-installer` we keep the modules in our repository. The reason for this is:

   * we don't support other than rpm builds, where `tito` helps a lot with release process
   * makes it easier to handle async releases
   * control over the update: we don't have CI set up for making sure the update haven't cause some breakage