Create a custom script that calls vulscan with the parameters you're after:
Example: c:\program files (x86)\landesk\ldclient\vulscan.exe /scan=0
Then add a call to shutdown the computer.
Example: shutdown -t 30 (30 seconds to wait to shutdown)
The part I'm not positive about however is whether the job will immediately run each command back to back or not.
If it does, that means vulscan would start, and then the computer would call to shutdown with a 30 second delay, so the scan wouldn't finish.
You could try writing in some loop logic that checks if vulscan.exe is still processing, and once is not processing, have it run shutdown.