[AudioServer] Fix CTS for volume groups based on non public streams

This CL fixes VolumeGroup CTS by preventing to set the volume per
stream for group associated to a non public stream type.

Bug: 136121584
Test: run cts-dev -m CtsMediaTestCase --test android.media.cts.AudioProductStrategyTest
run cts-dev -m CtsMediaTestCase --test android.media.cts.AudioVolumeGroupTest
run cts-dev -m CtsMediaTestCase --test android.media.cts.AudioVolumeGroupChangeHandlerTest
run cts-dev -m CtsMediaTestCase --test android.media.cts.AudioManagerTest#testPermissionsForVolumePerAttributes
run cts-dev -m CtsMediaTestCase --test android.media.cts.AudioManagerTest#testGetAndValidateProductStrategies
run cts-dev -m CtsMediaTestCase --test android.media.cts.AudioManagerTest#testGetAndValidateVolumeGroups
run cts-dev -m CtsMediaTestCase --test android.media.cts.AudioManagerTest#testSetGetVolumePerAttributesWithInvalidAttributes
run cts-dev -m CtsMediaTestCase --test android.media.cts.AudioManagerTest#testSetGetVolumePerAttributes
run cts-dev -m CtsMediaTestCase --test android.media.cts.AudioManagerTest#testVolumeGroupCallback

Change-Id: I53d9d2d4d7591300bf364d591412b548356cd118