Make blacklisted JS system_test.sh less flakey.
Make blacklisted JS system_test.sh less flakey.

crowell/modpagespeed_tmp,crowell/modpagespeed_tmp,crowell/modpagespeed_tmp,crowell/modpagespeed_tmp,crowell/modpagespeed_tmp,crowell/modpagespeed_tmp,crowell/modpagespeed_tmp