Adds E2E tests for soundtrigger stub HAL load/start/trigger/stop/unload

These tests can only be run with the stub HAL. The test's Android.mk
file excludes these tests when run without the flag
SOUND_TRIGGER_USE_STUB_MODULE=1

To run the stub HAL tests, run:
SOUND_TRIGGER_USE_STUB_MODULE=1 runtest \
--path ./frameworks/base/tests/SoundTriggerTests

Change-Id: Iac144c51b8a387e94ad25d283715842d46e6e618