Fix test collection for XSS lint tests.
Fix test collection for XSS lint tests.

This was failing before because DDT was trying to get an attribute
from an XSS Lint RuleSet object but that was throwing an exception
because the RuleSet object didn't have that attribute.

In python 2 such exceptions were automatically swallowed by the
getattr function but in python 3 they get raised.

msegado/edx-platform,eduNEXT/edunext-platform,eduNEXT/edx-platform,stvstnfrd/edx-platform,ESOedX/edx-platform,ESOedX/edx-platform,appsembler/edx-platform,appsembler/edx-platform,edx/edx-platform,cpennington/edx-platform,appsembler/edx-platform,angelapper/edx-platform,mitocw/edx-platform,eduNEXT/edx-platform,edx/edx-platform,stvstnfrd/edx-platform,stvstnfrd/edx-platform,appsembler/edx-platform,eduNEXT/edunext-platform,edx-solutions/edx-platform,stvstnfrd/edx-platform,edx-solutions/edx-platform,angelapper/edx-platform,arbrandes/edx-platform,arbrandes/edx-platform,eduNEXT/edunext-platform,angelapper/edx-platform,eduNEXT/edunext-platform,edx-solutions/edx-platform,cpennington/edx-platform,ESOedX/edx-platform,EDUlib/edx-platform,mitocw/edx-platform,cpennington/edx-platform,edx-solutions/edx-platform,msegado/edx-platform,edx/edx-platform,EDUlib/edx-platform,edx/edx-platform,msegado/edx-platform,msegado/edx-platform,ESOedX/edx-platform,cpennington/edx-platform,eduNEXT/edx-platform,mitocw/edx-platform,mitocw/edx-platform,arbrandes/edx-platform,EDUlib/edx-platform,EDUlib/edx-platform,eduNEXT/edx-platform,msegado/edx-platform,angelapper/edx-platform,arbrandes/edx-platform