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 is error 2, this should be !PvInitialize(). The function returns 0 when initialization is busy and thus waiting untill a camera is up should depend on it being 0.