Adding expected failure for test_compare_to_xls
Adding expected failure for test_compare_to_xls

- test_compare_to_xls requires verification of which data are correct
- Made the skip for test_shortest_path conditional


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kaustubhcs/PyOpenWorm,gsarma/PyOpenWorm,hnunner/PyOpenWorm,travs/PyOpenWorm,openworm/PyOpenWorm,openworm/PyOpenWorm,gsarma/PyOpenWorm