Merge github#887: app-admin/collectd: Version bump to v5.5.1

This PR bumps collectd to version 5.5.1 and fixes a raft of bugs.

See commit 3b459b6d37f22f9da2c070173756bf12de2591f0 for a lengthy explanation
concerning the changes involved.

Pull-Request: https://github.com/gentoo/gentoo/pull/887
Gentoo-Bug: https://bugs.gentoo.org/570766
Gentoo-Bug: https://bugs.gentoo.org/517060
Gentoo-Bug: https://bugs.gentoo.org/524400
Gentoo-Bug: https://bugs.gentoo.org/570778
Reporter: Thomas D <whissi@whissi.de>
Acked-by: Johan Bergström <bugs@bergstroem.nu>
Signed-off-by: Patrice Clement <monsieurp@gentoo.org>