CHEF-4086: Use "Host:" header value to construct returned URLs

 - CHEF-4086: Use "Host:" header value to construct returned URLs

Requires:
  - https://github.com/opscode/chef-pedant/pull/59
  - https://github.com/opscode/chef_objects/pull/50
  - https://github.com/opscode/omnibus-chef-server/pull/19

Notes:
  - I did not include the case where Hosts: is empty (and not missing).
  - How to even test this? Pedant won't catch all the cases, so additional unit testing is required.