fix test and exception handling in code

With python 2 it was possible to do exception[0][...] to recover
details about an exception.
It's no longer authorized with python 3.
Now, we must do something like exception.args or exception.urls.
fortunately this syntax also works with python 2.
So we use it for both.

tests/test_LdapCherry.py

@@ -185,7 +185,7 @@ class TestError(object):
             app.login(u'jwatsoné', u'passwordwatsoné')
         except cherrypy.HTTPRedirect as e:
             expected = 'http://127.0.0.1:8080/'
-            assert e[0][0] == expected
+            assert e.urls[0] == expected
         else:
             raise AssertionError("expected an exception")
 
@@ -197,7 +197,7 @@ class TestError(object):
             app.login(u'jwatsoné', u'wrongPasswordé')
         except cherrypy.HTTPRedirect as e:
             expected = 'http://127.0.0.1:8080/signin'
-            assert e[0][0] == expected
+            assert e.urls[0] == expected
         else:
             raise AssertionError("expected an exception")