CHEF-4235 make postgres port configurable

This PR is based on top of https://github.com/opscode/omnibus-chef-server/pull/21

And supercedes the patch here:
https://github.com/ketan/omnibus-chef-server/commit/f34a62aa916f77920ec9686beca3ef5e1e643767
which no longer applies due to other refactoring of the postgresql recipe.