This *kind of* addresses:

  https://bugzilla.redhat.com/show_bug.cgi?id=772395

(it doesn't eliminate the failure to start, but causes libvirt to give
a better idea about the cause of the failure).

If a guest uses a kvm emulator (e.g. /usr/bin/qemu-kvm) and the guest
is started when kvm isn't available (either because virtualization is
unavailable / has been disabled in the BIOS, or the kvm modules
haven't been loaded for some reason), a semi-cryptic error message is
logged:

  libvirtError: internal error Child process (LC_ALL=C
  PATH=/sbin:/usr/sbin:/bin:/usr/bin /usr/bin/qemu-kvm -device ? -device
  pci-assign,? -device virtio-blk-pci,? -device virtio-net-pci,?) status
  unexpected: exit status 1

This patch notices at process start that a guest needs kvm, and checks
for the presence of /dev/kvm (a reasonable indicator that kvm is
available) before trying to execute the qemu binary. If kvm isn't
available, a more useful (too verbose??) error is logged.