openni_capture sample: enable OpenNI2 if available
openni_capture sample: enable OpenNI2 if available

Sample works with OpenNI2 with minimal code changes (CAP_OPENNI -> CAP_OPENNI2)

opencv/opencv,opencv/opencv,apavlenko/opencv,apavlenko/opencv,apavlenko/opencv,apavlenko/opencv,opencv/opencv,apavlenko/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,apavlenko/opencv