Glance has dropped default policy.json [1] which
was used by "smart sources". We are fixing this by setting content
to empty dict, that way the only content deployed will be the one
provided by overrides, so that won't change current behaviour.
Additionally `glance_policy_content` has been introduced, which
eventually is going to replace `glance_policy_overrides` in the future.
[1] dd1975bd3e
Change-Id: I3f365684542b390ea02c08ab56f76a447f65a814
0f7971c9cb