(grnet) Move disk options before nic ones in kvm command

(grnet) Move disk options before nic ones in kvm command

Older versions of Ganeti did ensure that during startup
disk devices will be inserted before nic devices in PCI
configuration space. KVM inserts devices to PCI slots
depending on the order of command line options.

Upon migration kvm command options are re-generated based
on runtime files info. To be able to migrate instances
with old format runtime files put disk options before
NIC ones so that disk occupy the first pci slots available
and not the other way around.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>