Refactor the App Helper Library test strategy.

* The test base is open-sourced.
* The tests have a platform-agnostic layer.
* The tests are genericized on the interface.
* Depend on the system helpers for pkg clearing.

Bug: 30545159
Test: manual
Change-Id: Ie83e894bca58627e9fa4499fbd4faa3f740f1da9