Add an option to allow unattended system-only upgrades with `barracuda up-stable system` from cron.

To run automated system-only upgrades every Sunday, without upgrading any Aegir instance, you can now add these lines to your /etc/ctontab:

echo "17 5    * * 7   root    cd;wget -q -U iCab http://files.aegir.cc/BOA.sh.txt;bash BOA.sh.txt" >> /etc/crontab
echo "18 5    * * 7   root    barracuda up-stable system" >> /etc/crontab

Barracuda will send the upgrade report to the e-mail address defined as _MY_EMAIL in your /root/.barracuda.cnf file

You can configure it to run when you wish, of course, like everyday, or on Friday or Monday etc.

Just try to keep it running either before midnight or after 5 AM, to avoid collisions with other cron task.