libjpeg8 support on Ubuntu 12.04

Re. my first pull request and my inability to get the integration tests to install `libjpeg8-dev` on Ubuntu 12.04, it turns out it just needed to run `apt-get update` before trying to install `libjpeg8-dev` on that platform version so I've adjusted accordingly. Tests now use Berkshelf to install dependencies and `apt` is a dependency in the `metadata.rb` file and is included in the recipe.