[upower-0.99] power: Use logind to discover critical action availability

based on two upstream commits

https://git.gnome.org/browse/gnome-settings-daemon/commit/plugins/power/gsd-power-manager.c?h=gnome-3-12&id=0c5fd82a6ce25abca9a9d7018889bad8fc1c6057

and

power: Use logind to discover critical action availability