possible reasons to suspend:
 * lid
 * power button
 * soft button
 * inactivity
 * critical action
 * screen blanking

states possibly affecting action:
 * on AC
 * on battery

current policy locations:
 * lid:
    - systemd
    - gsd-power inhibits in some cases
 * power button:
    - gsd-media-keys: org.gnome.settings-daemon.plugins.power power-button-action
 * soft button:
   - gnome-shell: hardcoded to suspend (logind call)
 * inactivity
   on AC:
   - gsd-power: org.gnome.settings-daemon.plugins.power sleep-inactive-ac-type
   on battery:
   - gsd-power: org.gnome.settings-daemon.plugins.power sleep-inactive-battery-type
 * critical action:
   - upower: /etc/UPower/UPower.conf CriticalPowerAction (default: HybridSleep)
 * screen blanking:
   - gsd-power: hardcoded to suspend instead of just blanking the screen