Fix syntax for Varnish 3.

I know that this isn't the final solution, but it's a good place to start talking. Ubuntu 12.04 (which I know isn't the box you test with) uses Varnish 3. The `default.vcl.erb` template in `cookbooks-override/varnish/templates/default` assumes Varnish 2.

https://www.varnish-cache.org/docs/3.0/installation/upgrade.html was what I used to convert the syntax.

What's a reasonably platform-agnostic way to handle this?