Move policy_file option to oslo_policy group in devstack setup
Move policy_file option to oslo_policy group in devstack setup

"policy_file" option in DEFAULT group is deprecated, it is
recommended to move it to oslo_policy group, modify
devstack script to put it into right group.

Change-Id: If0665eaf813b1a2266b458503da6323caecaaa5c
Closes-bug: #1691689

openstack/searchlight,openstack/searchlight,openstack/searchlight