Add exception handler for previous deleted flavor.

An exception happens if a previous flavor is deleted and
'nova resize-revert' run, because 'nova resize-revert' does
not handle the deleted flavor.
And also we have the same problem in _update_usage_from_migration().
This patch fixes the problems.

How to reproduce the problem on DevStack:
  $ nova flavor-create sample 10 512 0 2
  $ nova boot --image cirros-0.3.0-x86_64-uec --flavor sample test01
  $ nova resize test01 m1.tiny
  $ nova flavor-delete 10
  $ nova resize-revert test01

Before applying this patch:
  $ nova resize-revert test01
  ERROR: The server could not comply with the request since it is
  either malformed or otherwise incorrect. (HTTP 400) (Request-ID:
  req-b0d3e016-9608-4a87-a0cc-44dfe00b25a1)
  $

After applying this patch:
  $ nova resize-revert test01
  ERROR: Flavor used by the instance could not be found. (HTTP 400)
  (Request-ID: req-ed4ce174-33f2-4258-b522-674a1023ea74)
  $

Fixes bug 1091490

Change-Id: I39dd23a7565ae66544e8bc2aa7ad3299eb61bfcc

nova/api/openstack/compute/servers.py

@@ -1024,6 +1024,9 @@ class Controller(wsgi.Controller):
         except exception.MigrationNotFound:
             msg = _("Instance has not been resized.")
             raise exc.HTTPBadRequest(explanation=msg)
+        except exception.InstanceTypeNotFound:
+            msg = _("Flavor used by the instance could not be found.")
+            raise exc.HTTPBadRequest(explanation=msg)
         except exception.InstanceInvalidState as state_error:
             common.raise_http_conflict_for_instance_invalid_state(state_error,
                     'revertResize')

nova/compute/resource_tracker.py

@@ -453,7 +453,12 @@ class ResourceTracker(object):
                 filtered[uuid] = migration
 
         for migration in filtered.values():
-            self._update_usage_from_migration(resources, migration)
+            try:
+                self._update_usage_from_migration(resources, migration)
+            except exception.InstanceTypeNotFound:
+                LOG.warn(_("InstanceType could not be found, skipping "
+                           "migration."), instance_uuid=uuid)
+                continue
 
     def _update_usage_from_instance(self, resources, instance):
         """Update usage for a single instance."""

nova/tests/compute/test_compute.py

@@ -4239,6 +4239,40 @@ class ComputeAPITestCase(BaseTestCase):
         instance_types.destroy(name)
         self.compute.terminate_instance(self.context, instance=instance)
 
+    def test_resize_revert_deleted_flavor_fails(self):
+        orig_name = 'test_resize_revert_orig_flavor'
+        orig_flavorid = 11
+        memory_mb = 128
+        root_gb = 0
+        vcpus = 1
+        instance_types.create(orig_name, memory_mb, vcpus, root_gb, 0,
+                              orig_flavorid, 0, 1.0, True)
+
+        instance = self._create_fake_instance(type_name=orig_name)
+        instance = db.instance_get_by_uuid(self.context, instance['uuid'])
+        instance = jsonutils.to_primitive(instance)
+        self.compute.run_instance(self.context, instance=instance)
+
+        old_instance_type_id = instance['instance_type_id']
+        new_flavor = instance_types.get_instance_type_by_name('m1.tiny')
+        new_flavorid = new_flavor['flavorid']
+        new_instance_type_id = new_flavor['id']
+        self.compute_api.resize(self.context, instance, new_flavorid)
+
+        db.migration_create(self.context.elevated(),
+                {'instance_uuid': instance['uuid'],
+                 'old_instance_type_id': old_instance_type_id,
+                 'new_instance_type_id': new_instance_type_id,
+                 'status': 'finished'})
+        instance = db.instance_update(self.context, instance['uuid'],
+                                      {'task_state': None,
+                                       'vm_state': vm_states.RESIZED})
+        instance_types.destroy(orig_name)
+        self.assertRaises(exception.InstanceTypeNotFound,
+                          self.compute_api.revert_resize,
+                          self.context, instance)
+        self.compute.terminate_instance(self.context, instance=instance)
+
     def test_migrate(self):
         instance = self._create_fake_instance()
         instance = db.instance_get_by_uuid(self.context, instance['uuid'])