Sleep immediately after returning from suspend

This is only necessary to apply the timeout to spurious wakeups, but
there is no concequence in doing it always as the sleep time after the
last wakeup source will come at least hysteresis_ms in the future.
Handle EBUSY from the power state write

The kernel may return EBUSY if it can't acquire the pm_mutex. Just loop
around and try again.
service: Allow extra arguments
Enable more informational messages
set stdout to line buffered

This is desirable when writing to the systemd journal.