Fails to resume after reboot.

[cweimann]

When it reboots it fails to rmdir /tmp/f-upgrade.lock so when the system starts up again it won't resume the upgrade. I have removed /tmp/f-upgrade.lock twice and run f-upgrade again twice now. Other than that it seems to work well. Not sure that this matters but I used it to upgrade from 10.3 to 10.4 on an old test VM.