Run ansiblecube at the first reboot.

[letompouce]

Since ansiblecube has a master tag, the preseed could drop a temporary /etc/rc.local to run it at the first reboot.

This way, a server is ready to get custom'ized. It doesn't save a lot of time, but it's still a progress in our plans to let the robots do all the job while we drink margaritas on the beach.