Expect _prev from glance.image_list_detailed

Glance changed recently to allow paging both ways
(forward and backward). Resulting openstack_dashboard change
broke the modal dialog in murano because we're only trying
to unpack images, _more. Patch adds _prev, but also tries
the older way if that fails.

Change-Id: I62237c15c082676afcc04ea2f94642049a8babde
Closes-Bug: 1339261
Merge "Expect _prev from glance.image_list_detailed"