Fixed. I had installed a preview repository from Red Hat for some not-yet-released libguestfs features (libguestfs-RHEL-7.1-preview). There were evidently changes to some release packages in the updates repository that were incompatible with the candidate packages in the preview repository cited above. I disabled the preview repo in /etc/yum.repos.d/..., uninstalled each of its packages, and re-installed the relevant packages (libvirt qemu-kvm qemu-kvm-tools virt-* spice-gtk spice-gtk-python spice-gtk-tools spice-gtk3-vala spice-xpi). Lesson learned: When you install 3rd party repositories you should reserve time for hand-holding your package management system. -- Charles Polisher