Pass the correct image to build_request_spec in conductor.rebuild_instance

If we're calling build_request_spec in conductor.rebuild_instance,
it's because we are evacuating and the instance is so old it does
not have a request spec. We need the request_spec to pass to the
scheduler to pick a destination host for the evacuation.

For evacuate, nova-api does not pass any image reference parameters,
and even if it did, those are image IDs, not an image meta dict that
build_request_spec expects, so this code has just always been wrong.

This change fixes the problem by passing a primitive version of
the instance.image_meta which build_request_spec will then return
back to conductor and that gets used to build a RequestSpec object
from primitives.

It's important to use the correct image meta so that the scheduler
can properly filter hosts using things like the
AggregateImagePropertiesIsolation and ImagePropertiesFilter filters.

Conflicts:
      nova/conductor/manager.py

NOTE(mriedem): Conflict is due to e211fca55a
not being in Ocata.

Change-Id: I0c8ce65016287de7be921c312493667a8c7f762e
Closes-Bug: #1727855
(cherry picked from commit d2690d6b03)
(cherry picked from commit dc44c48943)

nova/conductor/manager.py

@@ -712,8 +712,11 @@ class ComputeTaskManager(base.Base):
                     # RequestSpec object - probably because the instance is old
                     # We need to mock that the old way
                     filter_properties = {'ignore_hosts': [instance.host]}
+                    # build_request_spec expects a primitive image dict
+                    image_meta = nova_object.obj_to_primitive(
+                        instance.image_meta)
                     request_spec = scheduler_utils.build_request_spec(
-                            context, image_ref, [instance])
+                            context, image_meta, [instance])
                 elif recreate:
                     # NOTE(sbauza): Augment the RequestSpec object by excluding
                     # the source host for avoiding the scheduler to pick it

nova/tests/unit/conductor/test_conductor.py

@@ -1239,6 +1239,9 @@ class _BaseTaskTestCase(object):
             self.conductor_manager.rebuild_instance(context=self.context,
                                             instance=inst_obj,
                                             **rebuild_args)
+            bs_mock.assert_called_once_with(
+                self.context, obj_base.obj_to_primitive(inst_obj.image_meta),
+                [inst_obj])
             fp_mock.assert_called_once_with(self.context, request_spec,
                                             filter_properties)
             select_dest_mock.assert_called_once_with(self.context, fake_spec)