AudioManagerTest: skip testVolume for TV

TV devices are connected to audio devices that are typically fixed
or full volume, therefore causing incremental volume changes to be
disabled, but there are no APIs yet to query this, therefore we
skip the testVolume test altogether for TVs.
Also improve assert messages in testVolume.

Bug: 160531287
Test: atest CtsMediaTestCases:android.media.cts.AudioManagerTest#testVolume
Change-Id: I72afbda0cc2b9e501031001e7e4287692b8ea9b5
1 file changed