Make nova-ceph-multistore use policy.yaml
Make nova-ceph-multistore use policy.yaml

This changes our tweak of glance policy to use the new yaml format
instead of json. Glance needs to tweak this file too in some jobs,
and it's easier to do that in two places if the more modern yaml
format is used.

Change-Id: I4d4263987719d4885f114931130a71877f25d21e
Related-Bug: #1916926

mahak/nova,openstack/nova,openstack/nova,openstack/nova,mahak/nova,mahak/nova