ovs-external-ids: Better handle VIFs from recently resumed VMs

ovs-external-ids: Better handle VIFs from recently resumed VMs

XAPI doesn't provide a way to look up a VIF entry based on the name, so
we have to locate it by other methods.  Previously, we were breaking up
the name into the domid and device number.  Unfortunately, it can take
XAPI a few seconds to update the domid of the VM, when resuming from a
suspend.  Since we have the VIF UUID, we can just look up the needed
information directly based on that.

Bug #3930