Return the HTTP Location for newly created resources

To provide information about the location of a newly created resource
(201) the Ironic API now returns the URI for the new object in the HTTP
Location header.

A new function build_url() was created in the link.py by factoring out
part of the the Link.make_link() method so that we can reuse that part
of the code to build a URL without having to create a new Link object.

Partial-Bug: #1317044
Change-Id: I88b033d446aaed93fc90ab6497578d5cd729dea8
Merge "Return the HTTP Location for newly created resources"