System Reader cannot read system scope resources

[Oleksandr Kozachenko]

I created a user with project member role and assigned reader role with system_scope:all.
```
$ openstack role assignment list --names --system all --role reader
+--------+-------------------+-------+---------+--------+--------+-----------+
| Role | User | Group | Project | Domain | System | Inherited |
+--------+-------------------+-------+---------+--------+--------+-----------+
| reader | user1@Default | | | | all | False |
+--------+-------------------+-------+---------+--------+--------+-----------+
```
But this user can only list resources in his project.
For example, failed to list all servers in the system with the following error.
```
$ openstack server list --all
Policy doesn't allow os_compute_api:servers:detail:get_all_tenants to be performed. (HTTP 403) (Request-ID: req-0be7173f-83cc-4917-9735-82e31464da32)

```
In nova api log, I can see `system_scope: None` in policy check.
```
Policy check for os_compute_api:servers:allow_all_filters failed with scope check {'is_admin': False, 'user_id': 'c0f8017926b496459fa91995a502c68c', 'user_domain_id': 'default', 'system_scope': None, 'domain_id': None, 'project_id': '62a1872ed4a9ef9865311576145b3baa', 'project_domain_id': 'default', 'roles': ['reader'], 'is_admin_project': True, 'service_user_id': None, 'service_user_domain_id': None, 'service_project_id': None, 'service_project_domain_id': None, 'service_roles': []} authorize /var/lib/openstack/lib/python3.8/site-packages/nova/policy.py:192

```

Also failed to get other resources such as service, endpoints, users which requires system scope permission.
Seems system scope is not working at all.