VTS: changes for qti encoder plugins

QTI components were failing VTS under following conditions :
1) unsupported resolutions.
2) fetchGraphicBuffer failed

In all these cases, test should be skipped instead of getting marked as FAILED.

Test: VtsHalMediaC2V1_0TargetVideoEncTest -I default -C c2.qti.avc.encoder -P /sdcard/res/

Bug: 132405032

Change-Id: Icd020135ee735f9f976a3a2cadf8a7ef5e378feb