[CHEF-5075] Fix json_attribs and recipe_url load order.
Add comment about order
CHEF-5075: order matters for recipe_url

Add a test to ensure we maintain the order of fetching the tarball before loading JSON attributes
from a file that may be in that recipe tarball

Refactor slightly for the benefit of testing
Update CHANGELOG for #1627 / #1283 / CHEF-5075

Fixes #1627.
Fixes #1283.