DOC_CONTENTS=$(<"${FILESDIR}/README.gentoo-r2") This will not work since FILESDIR is not available in pkg_* when installing from binary package. Portage will also start to enforce that for source builds at some point. Plus, I think the value from src_install() persists, so there should be no reason to redefine it here.
commit ebfcee749d9e3ee01bb3d5b669d4ed49ce01b753 Author: Matthias Maier <tamiko@gentoo.org> Date: Fri Mar 17 15:18:00 2017 -0500 app-emulation/libvirt: Do not use FILESDIR outside of SRC_*, bug #612838 Package-Manager: Portage-2.3.3, Repoman-2.3.2