Ruby-based Depsolver over Erlang open_port

This is the initial work for a proof-of-concept of communication with the ruby-based depselector gem over erlang open_port. Further work includes:

* packaging the ruby executable for use in a running system (erchef)
* managing ruby processes as a pool
* modifying chef_wm to handle different return values / error messages
* further unit testing at the chef_objects level
* further testing at the ruby level