vte:2.90 slot is completely dead, people should use :2.91 slot when possible. Then, I would change the deps to 2.91 only (also the 9999 ebuild needs fixing as it's forcing 2.90 slot only) Thanks
commit fb982936adb33e13aaa87d5b2a53293e3242d285 Author: Matthias Maier <tamiko@gentoo.org> Date: Thu Dec 1 10:55:54 2016 -0600 app-emulation/virt-manager: drop vte:2.90 dependency, bug #595892 Package-Manager: portage-2.3.0