Fix wrong usage of extend in list_image_import_opts
Fix wrong usage of extend in list_image_import_opts

Review https://review.openstack.org/#/c/541740/ wrongly
used "extend" method in image_import_opts, this patch
fixes it.

Change-Id: I00375575d601ea6d970bb93c3f01f35c034976a2
Closes-Bug: #1748399

openstack/glance,openstack/glance,openstack/glance