Update oslo.policy to 1.20.0
Update oslo.policy to 1.20.0

Change-Id: I88e1eac842e5195f83331ea33a60396e0d049b93
Depends-on: Ia67e4bfdb63d7aa0dc6bbd6c1a841278fda88165

openstack/rpm-packaging,openstack/rpm-packaging