Add limit tests for system member role

From keystone's perspective, the ``member`` and ``reader`` roles are
effectively the same, isolating writeable limit operations to the
``admin`` role.

This commit adds explicit testing to make sure the ``member`` role
is allowed to perform readable and not writable limit operations.
Subsequent patches will incorporate:

 - system admin functionality
 - testing for domain users
 - testing for project users

Change-Id: I186251e77bf1b6459e0660da72f57bcdf799f319
Related-Bug: 1805372
Related-Bug: 1805880

keystone/tests/unit/protection/v3/test_limits.py

@@ -143,7 +143,6 @@ class _UserLimitTests(object):
 class SystemReaderTests(base_classes.TestCaseWithBootstrap,
                         common_auth.AuthTestMixin,
                         _UserLimitTests):
-
     def setUp(self):
         super(SystemReaderTests, self).setUp()
         self.loadapp()
@@ -171,3 +170,36 @@ class SystemReaderTests(base_classes.TestCaseWithBootstrap,
             r = c.post('/v3/auth/tokens', json=auth)
             self.token_id = r.headers['X-Subject-Token']
             self.headers = {'X-Auth-Token': self.token_id}
+
+
+class SystemMemberTests(base_classes.TestCaseWithBootstrap,
+                        common_auth.AuthTestMixin,
+                        _UserLimitTests):
+
+    def setUp(self):
+        super(SystemMemberTests, self).setUp()
+        self.loadapp()
+        self.useFixture(ksfixtures.Policy(self.config_fixture))
+        self.config_fixture.config(group='oslo_policy', enforce_scope=True)
+
+        system_member = unit.new_user_ref(
+            domain_id=CONF.identity.default_domain_id
+        )
+        self.user_id = PROVIDERS.identity_api.create_user(
+            system_member
+        )['id']
+        PROVIDERS.assignment_api.create_system_grant_for_user(
+            self.user_id, self.bootstrapper.member_role_id
+        )
+
+        auth = self.build_authentication_request(
+            user_id=self.user_id, password=system_member['password'],
+            system=True
+        )
+
+        # Grab a token using the persona we're testing and prepare headers
+        # for requests we'll be making in the tests.
+        with self.test_client() as c:
+            r = c.post('/v3/auth/tokens', json=auth)
+            self.token_id = r.headers['X-Subject-Token']
+            self.headers = {'X-Auth-Token': self.token_id}