Add nightly builds

[laurivosandi]

With butterknife serve running on the host we could generate snapshots automatically every night. The cron.daily could be used to achieve that and it would also report errors back to the host owner. For nightly build we would could execute butterknfie-nightly in the container to peform for example following steps on Ubuntu template:

• apt-get update
• apt-get upgrade
• apt-get dist-upgrade
• apt-get autoremove
• puppet agent --onetime

After butterknife-nightly finishes running we could simply issue butterknife lxc release. Once we have proper commit messages in place this snapshot could be tagged as nightly.