[stable-only] Add missing classes to cinderclient.v3

The QuotaSet class was never added to cinderclient.v3.quotas, and
the VolumeTransfer class was never added to cinderclient.v3.
volume_transfers.

Note: this fix is proposed directly to the stable branches, as the
issue was fixed differently in master (Xena development) when the
cinderclient.v2 classes were removed by change I335db5c1799e.

Change-Id: Ie00f068d7818e20683a0c242b51027d657382dd4
Closes-bug: #1938451
(cherry picked from commit 579846c7a4)

cinderclient/tests/unit/v3/test_v2_compatibility.py

@@ -0,0 +1,46 @@
+# Copyright (c) 2021 Red Hat, Inc
+#
+# All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import importlib
+import inspect
+
+from cinderclient.tests.unit import utils
+import cinderclient.v2 as cv2
+import cinderclient.v3 as cv3
+
+
+class v2_CompatibilityTest(utils.TestCase):
+
+    def test_all_v2_classes_are_v3_classes(self):
+        CV2 = 'cinderclient.v2'
+        CV3 = 'cinderclient.v3'
+
+        v2_class_names = []
+        for mod_name, mod_data in inspect.getmembers(cv2, inspect.ismodule):
+            mod = importlib.import_module(CV2 + '.' + mod_name)
+            v2_class_names.extend([cls_name for cls_name, cls_data
+                                   in inspect.getmembers(mod,
+                                                         inspect.isclass)])
+
+        v3_class_names = []
+        for mod_name, mod_data in inspect.getmembers(cv3, inspect.ismodule):
+            mod = importlib.import_module(CV3 + '.' + mod_name)
+            v3_class_names.extend([cls_name for cls_name, cls_data
+                                   in inspect.getmembers(mod,
+                                                         inspect.isclass)])
+
+        for cls_name in v2_class_names:
+            self.assertIn(cls_name, v3_class_names)

cinderclient/v3/quotas.py

@@ -16,6 +16,10 @@
 from cinderclient.v2 import quotas
 
 
+class QuotaSet(quotas.QuotaSet):
+    pass
+
+
 class QuotaSetManager(quotas.QuotaSetManager):
 
     def update(self, tenant_id, **updates):

cinderclient/v3/volume_transfers.py

@@ -19,6 +19,10 @@ from cinderclient import base
 from cinderclient.v2 import volume_transfers
 
 
+class VolumeTransfer(volume_transfers.VolumeTransfer):
+    pass
+
+
 class VolumeTransferManager(volume_transfers.VolumeTransferManager):
     def create(self, volume_id, name=None, no_snapshots=False):
         """Creates a volume transfer.