udisksd: Put drive to sleep

[appleynski]

While udisksd already does a great job of setting APM values at boot, I heavily miss a way to put a drive to sleep at boot time (same thing hdparm -Y does).

This feature is already available in udisks' GUI (Disks) as "Standby Now", however its setting is not persisted across reboots.

The only workaround I know of is to use hdparm to put a drive to sleep at boot time, but this solution causes race conditions with udisksd.