With this change, also refactored runtest as follows: Modified the
test suite schema and python implementation to have an inheritance
structure. Each test type has its own python module, which will
also handle the logic of running the test.
This change is to adapt runtest to the InstrumentationTestRunner change which
dumps coverage data to the app's local data folder, instead of a fixed file on
the sdcard.
Also fixed adb_interace.StartInstrumentationForPackage, added better handling
when generating coverage for tests with unknown coverage targets, and reduced
the duplicate definitions of the "coverage_targets.xml" definition file.
