Tests: Various enhancements and fixes in transcoding, encoding

- unit-timeside: Small enhancements in Error messages display
- unit-timeside: Remove 'assertSameList' function which seems equivalent to unittest assertItemsEqual. unittest.TestCase class does thus no more need to be override, propagate this change in every test_* modules.
- test_encoding and test_transcoding: refactoring + handling of expected failures (duration for loseless encoders, channels for voaacenc, ...) + run everything in pipes to handle properly the setup.