scenario button systemperl
adjust $scripts_dir if cpan_smoke_modules and/or cpan_recent_uploads2 cannot be found

This is to be able to copy cpan_smoke_modules_wrapper3 to, say, /tmp, and still
work with the default cpan_smoke_modules script.
swap pass/fail passes in systemperl scenario

Running tests with the system perl can take long, especially for
large dependency trees, so to have quick results, do the
(possibly fast) failing perls first.
use _scenario_hidemod_and_prereq instead of just _scenario_hidemod