Look for correct sources.list.d file for apt::ppa

In Ubuntu 15.10 the path of the apt sources file, which is generated by
apt-add-repository, changed to include the distid. This breaks apt::ppa
idempotency, since it does not recognize the repository is already
added.

Reported on puppet-users as well:
https://groups.google.com/forum/#!topic/puppet-users/YzeMyZYUo98