Depend on the same docker version everywhere

The dependency in the Berksfile has been set to '>= 0.25.0', but the
metadata dependency hasn't which makes Chef pick the old version
(0.24.2). This causes deployments to fail due to the 'source' method
being unavailable
Depend on the latest nginx recipe

This fixes a dependency issue with build-essential. All other packages
depend on build-essential >= 0.0.0, whereas nginx-2.2.2 depends on
build-essential ~> 1.4.0
Merge pull request #20 from bauglir/master

Updated dependencies break deployment
Remove nginx/docker cookbook version restriction
Use the default docker cookbook for docker install/configuration

The docker cookbook now handles a lot of the use cases for when various
dependencies need to be installed. It will also append users to the
docker group (while creating it if needed) for us.
Set the spec ubuntu version to 14.04
Install python-software-properties on 12.04
Strainer is obsolete. Remove Strainerfile
update gem dependencies for test-kitchen migration
Add a Guardfile for chefspec, foodcritic, and test-kitchen
Basic test-kitchen setup with Ubuntu 12.04 and 13.10 as converge targets
Update Berksfile(.lock) for Berkshelf v3
Add Ubuntu 14.04 as a converge target. Fix bad indentation on driver VM config
Add serverspec and busser. Update berkshelf min version