And use a 'file://' url for the custom manila image.
See also https://review.openstack.org/#/c/623330. These
are interdependent patches but no harm is done by merging
this one first and having 623330 depend on it since retrieval
of the image name is not working correctly anyways.
Partial-Bug: #1807969
Change-Id: Ib3a74d170f159dfbc38b5302f00800f3530f4921
(cherry picked from commit 6299ed5ed001ae2768ed2b954730b526b4053b2c)
758eaac8cc