Use SpawnIsSynchronousFixture in reschedule functional tests

We see that in successful tests that are usually running some
kind of negative or reschedule scenario that they will dump
a stacktrace to the subunit output buffer because
_allocate_network_async will raise an error. Too many of these
can eventually blow up the subunit output buffer and cause
tests to fail.

To guard against this, we use the SpawnIsSynchronousFixture in
the base class of two known test classes [1][2] that show a
stacktace with _allocate_network_async in successful runs. As a
result, one of the tests has to be fixed due to improper stubbing.

[1] UnsupportedPortResourceRequestBasedSchedulingTest
[2] PortResourceRequestReSchedulingTest

Change-Id: Ib18ecaebbeccc9c9cea32ca8949175fcea0414ac
Related-Bug: #1813147

nova/tests/functional/test_servers.py

@@ -36,6 +36,7 @@ from nova.compute import instance_actions
 from nova.compute import manager as compute_manager
 from nova import context
 from nova import exception
+from nova.network.neutronv2 import api as neutronapi
 from nova.network.neutronv2 import constants
 from nova import objects
 from nova.objects import block_device as block_device_obj
@@ -5506,6 +5507,9 @@ class PortResourceRequestBasedSchedulingTestBase(
                 FakeDriverWithPciResourcesConfigFixture())
 
         super(PortResourceRequestBasedSchedulingTestBase, self).setUp()
+        # Make ComputeManager._allocate_network_async synchronous to detect
+        # errors in tests that involve rescheduling.
+        self.useFixture(nova_fixtures.SpawnIsSynchronousFixture())
         self.compute1 = self._start_compute('host1')
         self.compute1_rp_uuid = self._get_provider_uuid_by_host('host1')
         self.ovs_bridge_rp_per_host = {}
@@ -6800,15 +6804,17 @@ class PortResourceRequestReSchedulingTest(
         # First call is during boot, we want that to succeed normally. Then the
         # fake virt driver triggers a re-schedule. During that re-schedule the
         # fill is called again, and we simulate that call raises.
-        fill = nova.scheduler.utils.fill_provider_mapping
+        original_fill = nova.scheduler.utils.fill_provider_mapping
+
+        def stub_fill_provider_mapping(*args, **kwargs):
+            if not mock_fill.called:
+                return original_fill(*args, **kwargs)
+            raise exception.ResourceProviderTraitRetrievalFailed(
+                uuid=uuids.rp1)
 
         with mock.patch(
                 'nova.scheduler.utils.fill_provider_mapping',
-                side_effect=[
-                    fill,
-                    exception.ResourceProviderTraitRetrievalFailed(
-                        uuid=uuids.rp1)],
-                autospec=True):
+                side_effect=stub_fill_provider_mapping) as mock_fill:
             server = self._create_server(
                 flavor=self.flavor,
                 networks=[{'port': port['id']}])
@@ -6823,5 +6829,5 @@ class PortResourceRequestReSchedulingTest(
 
         # assert that unbind removes the allocation from the binding
         updated_port = self.neutron.show_port(port['id'])['port']
-        binding_profile = updated_port['binding:profile']
+        binding_profile = neutronapi.get_binding_profile(updated_port)
         self.assertNotIn('allocation', binding_profile)