fixing working with test data and a small fix to init code

- set init value to `numsdev` to prevent use of uninitialized value
- stop use of 'workdir' and files from samples
- forcing use of 'opencv_extra' instead

**Note**: set **OPENCV_TEST_DATA_PATH** to full path to `opencv_extra/testdata` (`gitolite@code.opencv.org:opencv_extra.git`) before running the test!