Fix glance endpoint tests

Glance endpoints are now located under http_client after reworking
for glance blueprint common-client-library-2. Change located in
glanceclient commit I5addc38eb2e2dd0be91b566fda7c0d81787ffa75

Test support both glanceclient versions for backward compatibility.

Change-Id: Idba3a05bdb09674b44dcc21c9427b4b85a29a1f7