Remove legacy regeneration of RequestSpec in MigrationTask

Previously we regenerated the RequestSpec from details in the Instance
before we had the full original object available to us. That is no
longer necessary and means we will not honor some of the original
request. Remove that now.

Change-Id: I195d389ac59574724a5e7202ba1a17d92c53a676
Closes-Bug: #1675607

nova/conductor/tasks/migrate.py

@@ -33,7 +33,6 @@ class MigrationTask(base.TaskBase):
         self.scheduler_client = scheduler_client
 
     def _execute(self):
-        image = self.request_spec.image
         self.quotas = objects.Quotas.from_reservations(self.context,
                                                        self.reservations,
                                                        instance=self.instance)
@@ -46,13 +45,6 @@ class MigrationTask(base.TaskBase):
         scheduler_utils.populate_retry(legacy_props,
                                        self.instance.uuid)
 
-        # TODO(sbauza): Remove that RequestSpec rehydratation once
-        # scheduler.utils methods use directly the NovaObject.
-        self.request_spec = objects.RequestSpec.from_components(
-            self.context, self.instance.uuid, image,
-            self.flavor, self.instance.numa_topology,
-            self.instance.pci_requests, legacy_props, None,
-            self.instance.availability_zone)
         # NOTE(sbauza): Force_hosts/nodes needs to be reset
         # if we want to make sure that the next destination
         # is not forced to be the original host

nova/tests/unit/conductor/tasks/test_migrate.py

@@ -68,16 +68,8 @@ class MigrationTaskTestCase(test.NoDBTestCase):
         task = self._generate_task()
         request_spec_from_components.return_value = self.request_spec
         legacy_request_spec = self.request_spec.to_legacy_request_spec_dict()
-        expected_props = {'retry': {'num_attempts': 1,
-                                    'hosts': [['host1', None]]},
-                          'limits': {}}
         task.execute()
 
-        request_spec_from_components.assert_called_once_with(
-            self.context, self.instance.uuid, self.request_spec.image,
-            task.flavor, self.instance.numa_topology,
-            self.instance.pci_requests, expected_props, None,
-            None)
         quotas_mock.assert_called_once_with(self.context, self.reservations,
                                             instance=self.instance)
         sig_mock.assert_called_once_with(self.context, legacy_request_spec,