Fix Hanging Shutdown

[adghayes]

VxScan will sometimes shut down immediately after pressing the power button. Sometimes it will take 1 minute, sometimes 3. @jdVotingWorks identified the source of the issue and we ought to fix it. When power down takes a long time, it's not very clear on the screen, so the user is likely to just yank the power plug, which removes any benefit of a controlled shutdown.

https://votingworks.slack.com/archives/CJU9MSC6S/p1729274393689579

[amcmanus]

This will be fixed once votingworks/vxsuite-complete-system#433 is merged.