JSON formatted policy file support is deprecated

[Yasufumi Ogawa]

In oslo, policy formatted in json was deprecated while victoria. It causes so many warnings in the result of unittest.

```
JSON formatted policy_file support is deprecated since Victoria release. You need to use YAML format which will be default in future. You can use ``oslopolicy-convert-json-to-yaml`` tool to convert existing JSON-formatted policy file to YAML-formatted in backward compatible way: https://docs.openstack.org/oslo.policy/latest/cli/oslopolicy-convert-json-to-yaml.html.
```

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/758697

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/758697
Committed: https://git.openstack.org/cgit/openstack/tacker/commit/?id=82a8cac5d2a27d59bdd20352f553c7eba2e17c70
Submitter: Zuul
Branch: master

commit 82a8cac5d2a27d59bdd20352f553c7eba2e17c70
Author: Yasufumi Ogawa <email address hidden>
Date: Mon Oct 19 03:11:19 2020 +0000

    Fix warnings for deprecated JSON policy file

    In `oslo.policy`, JSON formatted policy file had been deprecated until
    Victoria release. Although it's still supported, recommended to use
    the newer YAML format [1].

    For Tacker, it uses `policy.json` in unittest and causes many warnings
    in the result which makes developers hard to find a problem.

    [1] https://docs.openstack.org/oslo.policy/victoria/admin/policy-json-file.html

    Closes-bug: #1900312

    Change-Id: I47f7d3e1c2425dc6bbdf0a9ae8e7bc28b99f0aae
    Signed-off-by: Yasufumi Ogawa <email address hidden>

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/tacker 5.0.0.0rc1 release candidate.