Add VTS test for validating audio effects config against XML schema

If the device contains /vendor/etc/audio_effects.xml (the new XML
format for the audio effects configuration), the test validates
this config against the schema contained in
audio/effect/2.0/xml/audio_effects_conf_V2_0.xsd
(pushed to the device by the VTS test runner)

Change-Id: Ib57d30e3c1e32ce5d74f906a216f9bb8f635a28c
Test: this is a test
Bug: 37492580