Add additional acceptance testing.

This work adds a test for every parameter in every class/define in apt.
Improve apt::force tests and ensure cleanup happens consistently.
Ensure apt::ppa fails on non-Ubuntu.
Fixes to make the tests run under Debian as well as Ubuntu.
Merge pull request #207 from apenney/add-params

Add additional acceptance testing.
Merge pull request #208 from apenney/ppa-debian

Ensure apt::ppa fails on non-Ubuntu.