Fix nullable data_plane_status reference in port OVO

data_plane_status is nullable so it might not be present
in the primitive. This adjusts the pop call to handle that
and adds a somewhat generic test to prevent a regression.

Change-Id: I1ffcd91fae2a06611a5b163033319081f96f211d

neutron/objects/ports.py

@@ -385,4 +385,4 @@ class Port(base.NeutronDbObject):
         _target_version = versionutils.convert_version_to_tuple(target_version)
 
         if _target_version < (1, 1):
-            primitive.pop('data_plane_status')
+            primitive.pop('data_plane_status', None)

neutron/tests/unit/objects/test_base.py

@@ -24,6 +24,7 @@ from oslo_db import exception as obj_exc
 from oslo_db.sqlalchemy import utils as db_utils
 from oslo_utils import uuidutils
 from oslo_versionedobjects import base as obj_base
+from oslo_versionedobjects import exception
 from oslo_versionedobjects import fields as obj_fields
 from oslo_versionedobjects import fixture
 import testtools
@@ -1417,6 +1418,14 @@ class BaseDbObjectTestCase(_BaseObjectTestCase,
                                 **remove_timestamps_from_fields(
                                     fields, self._test_class.fields))
 
+    def test_downgrade_to_1_0(self):
+        for obj in self.objs:
+            try:
+                obj.obj_to_primitive(target_version='1.0')
+            except exception.IncompatibleObjectVersion:
+                # the only exception we should allow is IncompatibleVersion
+                pass
+
     def test_get_object_create_update_delete(self):
         # Timestamps can't be initialized and multiple objects may use standard
         # attributes so we need to remove timestamps when creating objects