API v2: Allow GET on unowned images with show_image_direct_url

This fixes an issue where copy.deepcopy was being a called
on an ImmutableLocations object, causing a Forbidden to be
raised.

Change-Id: Ia7ac121478cf63d68bd5a3d91faa51a42afeb2fe
Closes-Bug: 1287888
Merge "API v2: Allow GET on unowned images with show_image_direct_url"