To expose the image location in the API for versions below Mitaka,
show_image_direct_url should be set to True. For Mitaka specifically,
show_multiple_locations should also be set.
This change sets both of these values when show_multiple_locations is
set in the charm.
Change-Id: Ibb3b6ecd92834f6345d21801942da0d3466d5bdc
Closes-Bug: #1645703