fixing cap_pvpapi interface

This PR tries to fix the following 3 reported issues
- http://code.opencv.org/issues/3946
- http://code.opencv.org/issues/3947
- http://code.opencv.org/issues/3948

Basically it enables use of monochrome AVT cameras AND lets the initialize wait long enough since newer cams have a longer initialization time!
This should actually be numCameras=PvCameraList(cameraList, MAX_CAMERAS, NULL); instead.
The reason is that we want an updated cameraList after a call to PvInitialize() or the list will be wrong.