Enhance SDK fixture for 0.34.0

As we work out the kinks in openstacksdk to smooth the road for nova's
usage thereof, and until openstacksdk can provide opaque fixtures that
it can keep up to date as its internals change, we've been needing to
stub things out incrementally.

This commit more aggressively mocks the piece of openstacksdk that
keeps changing under us. It effectively does what [1] does, but without
the get_endpoint() sanity check, which blows up in unit/functional test
because it tries to do real ksa auth.

[1] https://review.opendev.org/#/c/675135/

Change-Id: I1ef2ca51da2dc25026a2fbdcfb1ed5199aaa518b

nova/tests/fixtures.py

@@ -30,6 +30,7 @@ import futurist
 from keystoneauth1 import adapter as ksa_adap
 import mock
 from neutronclient.common import exceptions as neutron_client_exc
+from openstack import service_description
 import os_resource_classes as orc
 from oslo_concurrency import lockutils
 from oslo_config import cfg
@@ -2138,5 +2139,16 @@ class OpenStackSDKFixture(fixtures.Fixture):
     # https://storyboard.openstack.org/#!/story/2005475 is resolved.
     def setUp(self):
         super(OpenStackSDKFixture, self).setUp()
-        self.useFixture(fixtures.MockPatch(
-            'keystoneauth1.adapter.Adapter.get_api_major_version'))
+        real_make_proxy = service_description.ServiceDescription._make_proxy
+        _stub_service_types = {'placement'}
+
+        def fake_make_proxy(self, instance):
+            if self.service_type in _stub_service_types:
+                return instance.config.get_session_client(
+                    self.service_type,
+                    allow_version_hack=True,
+                )
+            return real_make_proxy(self, instance)
+        self.useFixture(fixtures.MockPatchObject(
+            service_description.ServiceDescription, '_make_proxy',
+            fake_make_proxy))