Workaround Fedora libvirtd issues on Xen instances

Fedora libvirtd fails to start on Xen instances (i.e. rackspace
instances) due to [1].  This works around the issue until it can be
fixed upstream.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1098376

Change-Id: I3790b5025982730263a6a84fce596e80f09efd5a
Merge "Workaround Fedora libvirtd issues on Xen instances"