Before reboot your machine you need to modify the boot order options of your machine. So on Oracle VM Manager console, right click on your machine and select "Edit"
with the following one (Boot Order: Disk). And click OK
From the Oracle VM Manager console right click on your machine and select "Stop". Click OK on the Confirmation window.
and when successfully stopped your job will have a "completed" status
Now "Edit" again your machine and change your "Boot order" option to boot on Disk