Release 2.0.0

Summary:
This is basically a bugfix release, plus the addition of `ensure` in
`apt::ppa` and changing the default release in `apt::force` to none. This
latter change is backwards-incompatible, but very minor.

Backwards-Incompatible:
- Change default value of `apt::force` from `'testing'` to `false`

Features:
- Add `ensure` to apt::ppa for absent use case

Bugfixes:
- Fix apt::force unable to upgrade packages from releases other than its original
- Removed a few refeneces to aptitude instead of apt-get for portability
- Removed call to getparam() due to stdlib dependency
- Correct apt::source template when architecture is provided
- Retry package installs if apt is locked
- Use root to exec in apt::ppa
- Updated tests and converted acceptance tests to beaker