Audio V4: Improve VTS error messages

This does not change the test logic or constraints.
It only improves the error messages.

Bug: 77307068
Test: atest VtsHalAudioV4_0TargetTest
Change-Id: I6c79ddd014d4ab8aba4f1d0b918888f83dfb63ad
Signed-off-by: Kevin Rocard <krocard@google.com>