CTS test for mpeg2 decoder bugfix

This also adds a MediaCodec-based test so we can test all available
codecs for a given file instead of only the one that MediaPlayer
happens to pick, and fixes some potential issues with the MediaPlayer
based test.

Bug: 25765591
Change-Id: I134a805fde363d55f847016fc3806c8b39b4e811
2 files changed