Moves some unit tests that were part of glance but should have
belonged to glance_store.
These tests are ported from
glance/tests/unit/test_store_image.py
Related-Bug: #1548902
NOTE(mriedem): As part of the backport we have to remove
the verifier=None kwargs from the assertions made in
test_backend since the verifier code didn't exist in
stable/liberty.
Change-Id: I688629d37e9146aef33fbc9bb6fd8780521e06ab
(cherry picked from commit 5faadde2d6)