Test system refactoring

cmpEps replaced on cmpEps2 to reduce code dublication;
Constants for cmpEps return values added.
fix for OpenCV issue #2815

- libavcodec issue
- some decoders alter AVCodecContext width/height values, in a wrong way
- eg. in issue 2815, vp6f decoder changes these values, resulting in distorted / invalid frames
- this patch forces default AVCodecContext values
Merge pull request #518 from asmorkalov:ts_refactor
Merge pull request #523 from taka-no-me:fix_2815