Oslo.policy is moving away from using json format policy files[1].
This patch updates the Octavia documentation, policy configuration file, and
legacy admin-or-owner policy file to be in yaml format.
Octavia will continue to honor and support the json format file as long
as oslo.policy does, but this patch will encourage new deployments
to use the yaml format.
[1] https://docs.openstack.org/oslo.policy/latest/admin/policy-json-file.html
Change-Id: I925cc05981e677c0552b18f845fdbc512d2af22c
fafabad042