Allow testing plugin easily with latest Vagrant

This is a method recommended in the Vagrant documentation that is able
to reduce the feedback loop of testing the plugin after making changes.
See: http://docs.vagrantup.com/v2/plugins/packaging.html

- Add Vagrant as development dependency
- Add Vagrantfile, for plugin testing
- Add Vagrant local data dir to Git ignore list
Use RSpec for automated testing

- Add RSpec as a development dependency
- Add RSpec configuration
Add unit spec for Config
Add Dep class
Expect Dep class in provisioner
Add #meet to configuration

The #meet method unifies the interface for local and remote deps. This
deprecates the now obsolete #local_dep and #remote_dep methods.
Merge pull request #10 from bradfeehan/meet

Unify local and remote deps, add specs