use the switch_root function in shutdown

removes code duplication

also move switch-root to shared
locale: fix sending PropertiesChanged for x11 keymap changed

The sd_bus_emit_properties_changed() call for x11 keymap changes lacks
commas.. whoops. Fix it! Now localed emits PropertiesChanged signals
again.
bus: don't skip interfaces in bus_message_map_properties_changed()

Skipping interfaces randomly without the caller specifying it is nasty.
Avoid this and let the caller do that themselves.