Fix volume creation from image with allowed_direct_url_schemes

Fix volume creation from image with allowed_direct_url_schemes

When CONF.allowed_direct_url_schemes is set to ['file'] and
Glance image has direct_url or locations metadata with 'file:///'
scheme, cinder tries to directly read the image data from the
local file. However, currently the code is broken because return
value from get_location() has been changed to a tuple.
This fixes the code so that it can handle the metadata correctly.

Change-Id: I39a12a31fbfbd3a9824c67391096f74406d8a749
Closes-Bug: #1437477