The vtkRenderWindow was never finalized which caused GLXBadDrawable
errors on application exit if using multiple QVTKRenderWindowInteractor.
This patch provides a cleanup mechanism to finalize the vtkRenderWindow
before its destruction/close preventing GLXBadDrawable errors. This
patch works in both embedded and non-embedded cases.

This patch also provides a test case for QVTKRenderWindowInteractor.

DDM: commit manufactured to force dashboard tests

Change-Id: Ie86d17fe7648868f8f1d5e4b00f52419d5f35a5b