weston-init: Use the module systemd-notify
Notify systemd of a running weston instead of fire and forget boot up.
Weston can be started using a special systemd-module that is called systemd-notify. This module notifies the systemd init system, of a running weston.
The previous startup scheme was starting the weston-start script and simply returning asynchronously. But the weston instance was not yet up and running. So a dependent systemd unit could not rely on weston being up and running.
By using the Type=notify
the systemd is correctly notified and a
dependent service can then connect to weston.
BCS 746-000079