[libvirt] [PATCH]: Add a flag to let live migration be persistent

As pointed out by Łukasz Mierzwa <l.mierzwa(a)gmail.com&gt;, it would be nice if there was an option to automatically make a domain persistent on the destination during a live migration. The attached patch adds this simple capability. Note that this has to be applied on top of my previous secure migration patch, otherwise you'll have conflicts. Signed-off-by: Chris Lalancette <clalance(a)redhat.com&gt;