[Merge] ~enr0n/ubuntu-release-upgrader:ubuntu/main into ubuntu-release-upgrader:ubuntu/main

[Nick Rosbrook]

DBUS_SESSION_BUS_ADDRESS is set in do-release-upgrade, so it is set correctly in this spot. When you test manually, you are entering at a different place (i.e. do-release-upgrade is not executed directly), so you need to set in manually, e.g.

sudo env DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus ./mantic
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https://code.launchpad.net/~enr0n/ubuntu-release-upgrader/+git/ubuntu-release-upgrader/+merge/452304
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