Remove Chef configuration from Berksfile

Deafulting to chef_api :config for cookbooks requires a Chef server.
Removed that option to default to opscode site for cookbooks so you can
use Vagrant without having to set up a Chef server first.
Merge pull request #19 from dmend/master

Remove Chef configuration from Berksfile
Merge pull request #18 from reaperhulk/master

import gpg key for barbican
pin postgresql cookbook to 3.2.1 for now to work around upstream bug

* upstream cookbook currently tries to install libpq-dev, which is not
  the right package name for RHEL-based distributions