I still think this exception should not be caught here (also `exit` should not be called in a library according to the style guide see: https://github.com/pyne/pyne/blob/staging/docs/devsguide/style_guide.rst#calling-exit). It would be better either to skip tests that need nuc_data (which is admittedly a lot of them) or let them fail. We still need a way to notify the user why the test was skipped but that's a separate issue.