Add default attributes and fix resource usage.

These attributes by default are all lazily interpolated. We want to give
the provisioning a chance to be able to modify the version or the site
name without hacking apart the cookbook.
Add vagrant-cachier plugin to speed up builds.

I am currently in Barbados right now and the Internet isn't all that
great. I don't want to be continually downloading the Chef debian
packages as it is taking a long ass time to iterate on changes.
Fix artifact location to deploy a tarball.

The artifact cookbook deploys tarballs only and not git
repositories. Perhaps this is something we can change in the upstream!