Add chef-vault to chefdk

* Creates chef-vault as a new software definition
* Adds chef-vault as a dependency of chefdk
* Add chef-vault to the appbundler list
laziness is a virtue unless copy/pasta

* libffi isn't a dependency of chef-vault.
Merge pull request #178 from jtimberman/jtimberman/chef-vault-definition

Add chef-vault to chefdk