vbox: handle 'saved' state of VMs

VirtualBox has 'saved' state for VMs saved by the hypervisor.
However, the state is treated as VIR_DOMAIN_NOSTATE by the vbox
driver, resulting that virsh shows 'no state' for saved VMs.

The fix treats the state as VIR_DOMAIN_SHUTOFF as same as
other domains such as qemu.

Signed-off-by: Ryota Ozaki <ozaki.ryota@gmail.com>

src/vbox/vbox_tmpl.c

@@ -1923,6 +1923,7 @@ static virDomainState vboxConvertState(enum MachineState state) {
         case MachineState_Stopping:
             return VIR_DOMAIN_SHUTDOWN;
         case MachineState_PoweredOff:
+        case MachineState_Saved:
             return VIR_DOMAIN_SHUTOFF;
         case MachineState_Aborted:
             return VIR_DOMAIN_CRASHED;