[devtools/testlib] avoid hidding AttributeError in create_user()
commit() might raise a AttributeError too.
Use getattr(req, 'cnx', req) instead, which is a form already used to get the real cnx
in some code:
cubicweb/rset.py:577: cnx = getattr(self.req, 'cnx', self.req)
cubicweb/schema.py:353: with getattr(_cw, 'cnx', _cw).security_enabled(read=False):
We could use if hasattr(req, 'commit') here too but it lead to 3 additionals lines.
Maybe we should have commit() and rollback() on
cubicweb.web.request.ConnectionCubicWebRequestBase too ?