Add system scope for admin auth

Keystone is moving away from using either project-scope or domain-scope
for the main cloud administrator user, and instead moving toward the
admin user having a role assignment on the "system" scope[1]. This will
mean that no particular project or domain is special, and instead the
cloud administrator scopes to the system in order to make
deployment-wide changes. Keystone has now migrated all of its policies
to understand system scope[2], and if a deployment sets
[oslo_policy]/enforce_scope=true in keystone.conf and uses the new
policies, an admin user scoped to the admin project will not be able to
create dynamic credentials for tempest.

This patch adds a new parameter ``[auth]/admin_system`` to indicate that
neither the ``admin_project`` or ``admin_domain`` parameters apply to
the admin user and that the user should instead authenticate with the
system scope. This also adds ``admin_user_domain_name`` so that the
admin user can be found in its domain (namespace) without setting
``domain_name``, and for completeness also adds
``admin_project_domain_name`` so that ``domain_name`` could be omitted
even if using project scope.

[1] http://specs.openstack.org/openstack/keystone-specs/specs/keystone/queens/system-scope.html
[2] https://bugs.launchpad.net/keystone/+bugs?field.status%3Alist=FIXRELEASED&field.tag=system-scope

Depends-on: https://review.opendev.org/739262

Change-Id: I840b273c37ca7cc4592c43813abfb424337e2836
diff --git a/tempest/tests/lib/common/test_cred_client.py b/tempest/tests/lib/common/test_cred_client.py
index 860a465..b99311c 100644
--- a/tempest/tests/lib/common/test_cred_client.py
+++ b/tempest/tests/lib/common/test_cred_client.py
@@ -43,6 +43,14 @@
         self.projects_client.delete_tenant.assert_called_once_with(
             'fake_id')
 
+    def test_get_credentials(self):
+        ret = self.creds_client.get_credentials(
+            {'name': 'some_user', 'id': 'fake_id'},
+            {'name': 'some_project', 'id': 'fake_id'},
+            'password123')
+        self.assertEqual(ret.username, 'some_user')
+        self.assertEqual(ret.project_name, 'some_project')
+
 
 class TestCredClientV3(base.TestCase):
     def setUp(self):
@@ -53,7 +61,7 @@
         self.roles_client = mock.MagicMock()
         self.domains_client = mock.MagicMock()
         self.domains_client.list_domains.return_value = {
-            'domains': [{'id': 'fake_domain_id'}]
+            'domains': [{'id': 'fake_domain_id', 'name': 'some_domain'}]
         }
         self.creds_client = cred_client.V3CredsClient(self.identity_client,
                                                       self.projects_client,
@@ -75,3 +83,31 @@
         self.creds_client.delete_project('fake_id')
         self.projects_client.delete_project.assert_called_once_with(
             'fake_id')
+
+    def test_get_credentials(self):
+        ret = self.creds_client.get_credentials(
+            {'name': 'some_user', 'id': 'fake_id'},
+            {'name': 'some_project', 'id': 'fake_id'},
+            'password123')
+        self.assertEqual(ret.username, 'some_user')
+        self.assertEqual(ret.project_name, 'some_project')
+        self.assertIsNone(ret.system)
+        self.assertEqual(ret.domain_name, 'some_domain')
+        ret = self.creds_client.get_credentials(
+            {'name': 'some_user', 'id': 'fake_id'},
+            None,
+            'password123',
+            domain={'name': 'another_domain', 'id': 'another_id'})
+        self.assertEqual(ret.username, 'some_user')
+        self.assertIsNone(ret.project_name)
+        self.assertIsNone(ret.system)
+        self.assertEqual(ret.domain_name, 'another_domain')
+        ret = self.creds_client.get_credentials(
+            {'name': 'some_user', 'id': 'fake_id'},
+            None,
+            'password123',
+            system={'system': 'all'})
+        self.assertEqual(ret.username, 'some_user')
+        self.assertIsNone(ret.project_name)
+        self.assertEqual(ret.system, {'system': 'all'})
+        self.assertEqual(ret.domain_name, 'some_domain')