Automatically create laptopped vagrant boxes.

Vagrant boxes can be created automatically after a successful run of the
laptop test suite. These vagrant boxes are published to
[vagrantcloud](http://vagrantcloud.com/thoughtbot/) and should be a solid
start on a vagrant dev box suitable for modern ruby and ruby-on-rails
development.

Improvements include:

* Vagrantfiles fixed to have predictable names
* test/runner.sh now knows how to publish a box to s3
* Secrets for publishers extracted into ~/.laptop.secrets
* Error reporting improvements
* Full documentation on creating new base boxes

We now require vagrant >= 1.5.0 to use the automated test suite built into
laptop.