[Merge] ~nteodosio/update-manager:no-inhibit into update-manager:main

[Nathan Teodosio]

Why is it not ideal? I can't see any scenario worse than Update Manager being invoked again in a subsequent boot to finish what was in this manner interrupted. Maybe you have a particular concrete case in mind that I'm failing to notice. 

On the one hand, shutting down if Apt itself is not blocking it should be safe, and on the other, the behavior of silently ignoring a shutdown request is bound to be confusing/frustrating. I'd lean on the side of leaving the user to his will, if it is not harmful.

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https://code.launchpad.net/~nteodosio/update-manager/+git/update-manager/+merge/497846
Your team Ubuntu Core Development Team is requested to review the proposed merge of ~nteodosio/update-manager:no-inhibit into update-manager:main.