CameraService: Add unit test for stuck HAL at startup

New test verifies that getService is not called during camera service
startup, to make sure it can't get stuck if the camera HAL isn't
initializing properly.

Test: New test passes with new tryGetService code; test fails with
older camera service code.
Change-Id: I67b3fe392e8cc6961c33abf25e961a8e2df7d7b5