If the last location of the image is removed, image transitions back to queued.
This allows user to upload new data into the existing image record. By
preventing removal of the last location we prevent the image transition back to
queued.
This change also prevents doing the same operation via replacing the locations
with empty list.
SecurityImpact
DocImpact
APIImpact
Conflicts:
glance/tests/unit/v2/test_images_resource.py
Change-Id: Ieb03aaba887492819f9c58aa67f7acfcea81720e
Closes-Bug: #1525915
(cherry picked from commit e9e45baa9aaf58e69964419b6b4fb2048d115a0c)