https://bugzilla.redhat.com/show_bug.cgi?id=1149445

If the domain requests usage of the genid functionality,
then add the QEMU '-device vmgenid' to the command line
providing either the supplied or generated GUID value.

Add tests for both a generated and supplied GUID value.
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>
ACKed-by: NMichal Privoznik <mprivozn@redhat.com>