Add migration network support.

Add additional parameter to vmMigrate to support dedicated migration network
http://www.ovirt.org/Features/Migration_Network

Change-Id: I17d760c7421e765454e13ee5b7d8be23e6b7e383
Signed-off-by: Igor Lvovsky <ilvovsky@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/11795
Tested-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>