Comment 2 for bug 1590838

Ah, I just noticed that immediate shutdowns work fine. Scheduled shutdowns however are handled by logind, and that requires dbus. I'm afraid this won't change.

This has been "fixed" in yakkety by pulling libpam-systemd and consequently dbus into the container images, as we were able to make init/systemd-sysv/systemd non-essential. This is quite an intrusive change though, and not suitable for backporting.

So for now I'm afraid you need to install libpam-systemd if you need scheduled shutdowns.