[vtkusers] QVTKOpenGlWidget black screen and tests FAILED

[Utkarsh Ayachit]

> When i remove lines, display work fine :
> vtkRenderWindowInteractor with QVTKOpenGLWidget is not compatible ?

That's correct. You're better off letting QVTKOpenGLWidget create the
interactor for you. Calling
vtkSmartPointer<vtkRenderWindowInteractor>::New() will create platform
specific interactor, eg. vtkWin32RenderWindowInteractor which is not
compatible with `vtkGenericOpenGLRenderWindow` requried by
QVTKOpenGLWidget.

Utkarsh