sniffer + py3: handle error messages correctly

Author: tony

scent.py

@@ -27,7 +27,7 @@ def execute_nose(*args):
     try:
         return main()
     except SystemExit as x:
-        if x.message:
+        if hasattr(x, 'message'):
             print("Found error {0}: {1}".format(x.code, x.message))
             return not x.code
         else: