Insufficient permissions for policy files are not handled

[Vadym Markov]

Issue affects Horizon. Tested on Queens Devstack, but seems to affect any release and deployment.

Steps to reproduce:
1. chmod 000 ~/horizon/openstack_dashboard/conf/cinder_policy.json
2. Set DEBUG = False in ~/horizon/openstack_dashboard/local/local_settings.py
3. Restart Apache service
4. Log in to Horizon

Expected behavior:
Left panel is present, probably except some dashboards related to volumes

Actual behavior:
Left panel is absent, screenshot attached

in this case, policy loading fails at https://github.com/openstack/horizon/blob/master/openstack_auth/policy.py#L67 It logs traceback as warning

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/oslo.policy/+/670571
Committed: https://opendev.org/openstack/oslo.policy/commit/9919f1317c037163d0f31232991cca261881b66b
Submitter: "Zuul (22348)"
Branch: master

commit 9919f1317c037163d0f31232991cca261881b66b
Author: BubaVV <email address hidden>
Date: Thu Jul 11 17:57:47 2019 +0300

    Correctly handle IO errors at policy file load

    For now, policy file unaccessible due to access permission leads to
    silent failure without any notifictaion. Side effects of it are also
    affected by policy caching and might be quite confusing, like periodic
    disappearing of Horizon panels. Proposed patch added handling of such
    errors.

    Closes-bug: #1836390
    Change-Id: I0d67b6e7c2dcaa63d6bb807f013e5e7334efc715

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/oslo.policy 3.8.0 release.