intermittent cinema test failures on tylo from vtkThreadedImageWriter

The CoProcessingFullWorkflowCinema* tests intermittently hang and timeout on tylo, our windows python 3 tester. Debugging on the machine indicates that the hang occurs inside this line: https://gitlab.kitware.com/paraview/paraview/blob/master/ThirdParty/cinema/paraview/tpl/cinema_python/adaptors/paraview/pv_introspect.py#L487 when we construct a cinema store to work with and in particular when we initialize the VTK threaded image writer https://gitlab.kitware.com/paraview/paraview/blob/master/ThirdParty/cinema/paraview/tpl/cinema_python/database/raster_wrangler.py#L80

Be warned, there are Heisenbug aspects here, inserting prints before the code in question makes it pass more often, and perhaps every time.