New Location APIs

There is an OSSN[1] regarding the issues with "show_multiple_locations" parameter. If we enable "show_multiple_locations" (defaults to False), and the policies for add (set_image_location), get(get_image_location), remove(delete_image_location) are set for non-admins then non-admin users can modify location data to corrupt the image. The "show_multiple_locations" config option is needed by cinder to get/add locations for optimizations in path of creating a bootable volume from image, uploading volume to image etc.

[1] OSSN-65 : https://wiki.openstack.org/wiki/OSSN/OSSN-0065