System startup ready detection is based on init-done flag file

Support functionality in filewatcher module hides the details of
processing inotify events from glib io watch.

Display plugin uses filewatcher to unblock late suspend when
/run/systemd/boot-status/init-done flag file is created.

If /run/systemd/boot-status directory does not exist when mce is
started up, mce waits uptime to reach 60 seconds before unblocking
late suspend.

In any case late suspend is blocked for 10 after mce startup.