Skip some GAPI tests if VideoCapture is not capable to playback video

[asmorkalov]

Relates to #17470

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under OpenCV (BSD) License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or other license that is incompatible with OpenCV
• The PR is proposed to proper branch
• There is reference to original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

[dmatveev]

Thanks! Should it be findDataFile(..., false) instead?

I also added an instruction on running tests, can you please check if it works for you? https://github.com/opencv/opencv/wiki/Graph-API

[asmorkalov]

@dmatveev thanks for the instruction. The issue is related not to files search, but build configuration. FFmpeg and other video decoding back ends are not available during cross compilation. findDataFile can find file, but VideoCapture raises exception and test fails. I fixed only cases where VideoCapture is created in the test itself, but not hidden inside of G-API module.

[dmatveev]

@asmorkalov got it now, thanks!