Merge github#845: app-benchmarks/bonnie++: fixes a couple of bugs and bump to EAPI 6.

This PR fixes 3 bugs and updates bonnie++ to EAPI 6 courtesy of Göktürk Yüksek.

Pull-Request: https://github.com/gentoo/gentoo/pull/845
Gentoo-Bug: https://bugs.gentoo.org/show_bug.cgi?id=309319
Gentoo-Bug: https://bugs.gentoo.org/show_bug.cgi?id=431684
Gentoo-Bug: https://bugs.gentoo.org/show_bug.cgi?id=515334

Reporter: Göktürk Yüksek <gokturk@binghamton.edu>
Acked-by: David Seifert <soap@gentoo.org>
Signed-off-by: Patrice Clement <monsieurp@gentoo.org>