The ebuild now in portage is somewhat outdated. Not only has there a major rewrite of febootstrap (version 3) it has also changed its name to supermin (version 4 of febootstrap). Please update the ebuild and the name. I will look at the ebuild in the next days to find out what needs to be changed.
Also, this requires yum... that is unmaintained, outdated and vulnerable... maybe we should treeclean this if noone wants to take care of this and yum :/
commit eacc69bdbad136963da6a328cfc097d566082138 Author: Michał Górny <mgorny@gentoo.org> AuthorDate: Mon Aug 14 23:20:28 2017 Commit: Michał Górny <mgorny@gentoo.org> CommitDate: Mon Aug 14 23:24:33 2017 dev-util/febootstrap: Remove last-rited pkg, #541410