test/jsl.conf: ignore functions not always returning a value

what's wrong with this anyway
5 jobs for for_testrunner_2 in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

00:53:49

failed ERP5.UnitTest-Master

01:26:00

failed ERP5.UnitTest-Master.Medusa

01:16:48

passed SlapOS.Eggs.UnitTest-Master.Python2

00:21:28

passed SlapOS.Eggs.UnitTest-Master.Python3

00:09:27