BUG: Fix qMRMLVolumePropertyNodeWidgetTest1

This commit fixes the failing test by ensuring the vtkRenderingContextOpenGL
module is initialized.

The following error was occurring on all three platforms:

// ----------
Generic Warning: In /path/to/VTKv6/Rendering/Context2D/vtkContextDevice2D.cxx, line 27
Error: no override found for 'vtkContextDevice2D'.
// ----------

For more details, see:
http://www.vtk.org/Wiki/VTK/Build_System_Migration#How_Implementation_Modules_Are_Initialized
http://www.vtk.org/Wiki/VTK/VTK_6_Migration/Factories_now_require_defines

Finally, let's also note that the test executable was compiled with:

-DvtkRenderingContext2D_AUTOINIT="1(vtkRenderingContextOpenGL)"
-DvtkRenderingCore_AUTOINIT="4(vtkInteractionStyle,vtkRenderingFreeType,vtkRenderingFreeTypeOpenGL,vtkRenderingOpenGL)"
-DvtkRenderingFreeType_AUTOINIT="1(vtkRenderingFreeTypeFontConfig)"
-DvtkRenderingVolume_AUTOINIT="1(vtkRenderingVolumeOpenGL)"

and was linked against vtkRenderingContextOpenGL.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23686 3bd1e089-480b-0410-8dfb-8563597acbee