Update bornagain import in PyCore tests

Tests/Functional/Python/PyCore/intensitydata.py

Tests/Functional/Python/PyCore/intensitydata_io.py

Tests/Functional/Python/PyCore/intensitydata_io_tiff.py

Tests/Functional/Python/PyCore/mesocrystal1.py

Tests/Functional/Python/PyCore/polmagcylinders1.py

Tests/Functional/Python/PyCore/polmagcylinders2.py

Tests/Functional/Python/PyCore/sliced_composition.py

Tests/Functional/Python/PyCore/sliced_spheres.py

Tests/Functional/Python/PyCore/transform_BoxComposition.py

Tests/Functional/Python/PyCore/transform_CoreShellBox.py

Tests/Functional/Python/PyCore/transform_box.py

Tests/Functional/Python/PyCore/transform_cube.py

Tests/Functional/Python/PyCore/utils.py