Add enforce_scope setting support for Glance

Glance started moving to new RBAC and glance-tempest-plugin
and Tempest need to set few configuration to enable the
scope checks on glance side and so does on Temepst side to tell
glance is ready with scope checks so that test can be run with
scoped token.

Conflicts:
     lib/tempest

Change-Id: I09f513d08212bc80a3a86a750b29b1c6625d2f89
(cherry picked from commit 8c930492)