increase epsilon for TVL1 sanity test
increase epsilon for ResizeSameAsHost test
use downscaled frames in FGDStatModel test
fix BGR->BGR5x5 color convertion
fix CUDA cvtColor after corresponding change in CPU version

see https://github.com/Itseez/opencv/pull/3137
Merge pull request #3143 from jet47:cuda-cvt-color-fix
Merge pull request #3109 from jet47:gpu-test-fixes