[Merge] ~dgadomski/ubuntu/+source/gdm3/+git/lp1782152:unblock-sigusr1 into ~ubuntu-desktop/ubuntu/+source/gdm3:ubuntu/bionic

[Iain Lane]

Please make sure to update the changelog too
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https://code.launchpad.net/~dgadomski/ubuntu/+source/gdm3/+git/lp1782152/+merge/353089
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