Use a file that obviously doesn't exist by default

That way it will be obvious that sbws isn't really going to try to
log to /nonexist and that sbws must set this option for real elsewhere.

sbws/config.log.default.ini

@@ -60,4 +60,4 @@ formatter = sbwssys
 # which is the desired behaviour
 # dunno if there is a way to have log file as a variable
 # setting one as default
-args = ('sbws.log',)
+args = ('/nonexist',)