Comment 2 for bug 1286256

Note that bug https://bugs.launchpad.net/nova/+bug/1286257 is open on the issue of using force_tcg when libvirt_type=qemu. This bug is explicitly about waiting forever for the libguestfs process. Since force_tcg isn't available in any shipping version of libguestfs in either Ubuntu, RHEL, or Fedora, I think that timing out this operation gracefully is going to be an important fix.