This commit adds full coverage for the apt module as it currently exists. It
adds rspec-puppet tests for the defines (apt::builddep, apt::force, apt::pin,
apt::ppa, apt::source) and classes (apt, debian::testing, debian::unstable,
apt::params, apt::release).
This commit adds test coverage for apt::ppa.
This test coverage is suficient to verify the
code changes that resolve the issue with
aptitude update not being called when ppas were
added (#10451).