From Fedora Project Wiki
Initial setup on a Trimslice. I had trouble getting the display to work and didn't have a serial console. The suggestion to blank out the root password doesn't work on its own. You would also need to set PermitEmptyPasswords yes in /etc/ssh/sshd_config to login password less. Since that is a bit unsecure maybe another suggestion would be to put a /root/.ssh/authorized_keys file on the image before booting. That way one can ssh in as root and run initial-setup by hand.