Fix ability to generate object hashes in test_objects.py

Change https://review.openstack.org/#/c/114260/3 broke the ability to
generate object hash codes by setting GENERATE_HASHES in the
environment.

Change-Id: I08e015b44ac12655d33e0b04d5608d68c1f13270
Merge "Fix ability to generate object hashes in test_objects.py"