Setup only production database?

@mlafeldt: We could probably simplify [this code](https://github.com/elm-city-craftworks/practicing-ruby-cookbook/blob/master/recipes/_postgresql.rb#L16-L29) as well as the attributes file if we don't bother to create the test and development DBs.

Want to make that change? I could take care of it myself once I've got the article mostly written up, or you could patch it sooner if you'd like.