The GetNumVirtualDevices API that was recently added to
virtualaudio can be used to eliminate the synchronization
issues that AudioDeviceTests faces, so this set of tests
can now be re-enabled.

Test: re-adds 67 test cases; no production code change

MTWN-293 #done

Change-Id: I6d4618a52835f2ef388bed1dddef9491fc2e2b8d