Remove usage of "six.exec_"
Remove usage of "six.exec_"

RafaelPalomar/girder,manthey/girder,RafaelPalomar/girder,RafaelPalomar/girder,girder/girder,Kitware/girder,Kitware/girder,RafaelPalomar/girder,RafaelPalomar/girder,manthey/girder,girder/girder,girder/girder,Kitware/girder,girder/girder,manthey/girder,manthey/girder,Kitware/girder