Add skeleton of CarAudioManager test

Tests only that the getExternalSources call doesn't crash for now.
We'll want to add volume and fade/balance tests here as well.

Test: runtest -x packages/services/Car/tests/carservice_test/src/com/android/car/CarAudioManagerTest.java
Change-Id: I374fcd938b4d4d77de9a7bd7cb2b077b61981a6d
2 files changed