Refactor audiopolicymanager_tests to check 'getOutputForAttr'

The helper method 'getOutputForAttr' may raise a test error
which needs to be checked by the calling test using
'ASSERT_NO_FATAL_FAILURE' macro wrapper.

Flag: EXEMPT test refactoring
Bug: 414259900
Test: atest audiopolicy_tests
Change-Id: I3b0bc54a5ffbbdc073b5150d6e16483cde96fbfd