I used the following ebuild to install grub https://gitweb.gentoo.org/repo/gentoo.git/tree/sys-boot/grub/grub-2.02_beta2-r9.ebuild and was expecting files such as grub2-install, etc. in /usr/sbin. Now the binaries are /usr/sbin/grub-*. If it's a change in upstream then maybe the ebuild comnents and warnings should be updated.
This was announced in a news item a couple weeks ago. https://gitweb.gentoo.org/data/gentoo-news.git/tree/2016-08-11-grub2_multislot_default/2016-08-11-grub2_multislot_default.en.txt
commit 6b6dc3200101e816b21bed0be6b795421956f9bf Author: Mike Gilbert <floppym@gentoo.org> Date: Wed Aug 24 14:11:19 2016 -0400 sys-boot/grub: update postinst warnings for multislot Package-Manager: portage-2.3.0_p22 sys-boot/grub/grub-2.02_beta2-r9.ebuild | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)