Add specs for for package, pip and source recipes; minor fix to default spec

ChefSpec tests for the package, pip and source recipes; remove stub from default spec not needed since 213c37e5.

I wrote my own version of specifying the python package files via an attribute... then I saw there were already two pull requests to do that.  These are the specs I wrote for my implementation; hopefully they'll be useful when adding #58 and/or #90.

Thanks for considering this pull request.