Audio Test Harness - Small Changes to Base Service and sets up Presubmit Tests: - Refactors AudioTestHarnessImpl to make use of a static factory method for instantiation. - Adds test to ensure that static factory method returns non-null always. - Adds TEST_MAPPING to ensure tests are run in Presubmit. Change-Id: I71c89b30e5ae8be4d677c1189c342a62d0bb444d Test: Unit Tests in this CL Bug: 168814242