Fix context from_dict() for system_scope

A previous patch[1] added "system_scope" to the context for to_dict()
but the from_dict() method was not updated. This caused the
system_scope to always be None.
This patch corrects that by adding "system_scope" to the list of
values that may need to be extracted from the context dict.

[1] https://review.opendev.org/c/openstack/oslo.context/+/530509

Change-Id: Ica23d5c4183a692de3cb65a7ad72b19f47988ca6
(cherry picked from commit 8290621b05)
(cherry picked from commit 7187c672d4)

oslo_context/context.py

@@ -419,6 +419,7 @@ class RequestContext(object):
                           values.get('project_domain_name'))
         kwargs.setdefault('is_admin_project',
                           values.get('is_admin_project', True))
+        kwargs.setdefault('system_scope', values.get('system_scope'))
         for key in cls.FROM_DICT_EXTRA_KEYS:
             kwargs.setdefault(key, values.get(key))
         return cls(**kwargs)

oslo_context/tests/test_context.py

@@ -143,7 +143,8 @@ class ContextTest(test_base.BaseTestCase):
             "request_id": "request1",
             "global_request_id": "req-uuid",
             "resource_uuid": "instance1",
-            "extra_data": "foo"
+            "extra_data": "foo",
+            "system_scope": "all"
         }
         ctx = context.RequestContext.from_dict(dct)
         self.assertEqual(dct['auth_token'], ctx.auth_token)
@@ -163,6 +164,7 @@ class ContextTest(test_base.BaseTestCase):
         self.assertEqual(dct['domain_name'], ctx.domain_name)
         self.assertEqual(dct['user_domain_name'], ctx.user_domain_name)
         self.assertEqual(dct['project_domain_name'], ctx.project_domain_name)
+        self.assertEqual(dct['system_scope'], ctx.system_scope)
 
     def test_from_dict_unknown_keys(self):
         dct = {

releasenotes/notes/Fix-system-scope-from_dict-29615af90723ba4d.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    Fixes context from_dict() to properly handle system_scope.