How to force Mac to into dirty shutdown state on every power off?

Make sure you only shut down with shutdown -u, and be sure to disconnect power within the next 5 minutes. And, of course, make sure to keep "Start up automatically after a power failure" checked in System Preferences > Energy Saver.

If you try to keep that "dirty" bit set when doing a normal shutdown, it will automatically reboot the moment it finishes shutting down, unless you can magically yank power at just the right moment.

Apple's only modern hardware designed to be booted remotely is the Xserve server, which supports Lights Out Management (LOM). See ipmitool(1) for more information.