vm: return diskMapping on status()

status() is used by API.Global.getVMList and should return also the disk
mapping retrieved by the guest agent.

Reviewed-On: http://gerrit.ovirt.org/#/c/34636/ - Schema changes
Reviewed-On: http://gerrit.ovirt.org/31700
Change-Id: Ia68ff3c36ba91cde893876a16fc6702419a60d49
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1063597
Signed-off-by: Liron Aravot <laravot@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/33197
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>