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 be changed back to PvInitialize() without checking the return value.
The reason is that calls to several PVAPI cameras will fail because PvInitialize() is already initialized after the first camera is opened. The lack of checking for the return code will not effect code as later only there are enough traps to catch for problems