virt: graphdev: handle ticket for multiple devices

This patch extends the ticket support for the
multiple graphics devices scenario.

This is done by extending the VM.updateDevice API
to support the Graphics Devices in addition to the
Network Devices. The parameters which can be updated
are the one which allow to set a ticket
for graphics.

Change-Id: I62f56ea47399b0d26aafce053ea1201457564b73
Signed-off-by: Francesco Romani <fromani@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/26897
Reviewed-by: Michal Skrivanek <michal.skrivanek@redhat.com>
Reviewed-by: Vinzenz Feenstra <vfeenstr@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>