Using portage's secpass instead of look at uid

We need to write to overlays and of usersync is set in FEATURES, root is
not the dedicated user to write into overlays. Additionally on Gentoo
Prefix, uid is usually not 0 and that's needed for EAPI 4 support.
Issue a warning instead of error when secpass=0
Merge pull request #11 from Miriup/master

Issue 1: Allow non-root to run program