Fix issues deleting instances in RESIZED state

DB API call migration_get_by_instance_and_status requires admin
context...and it'll also raise an exception if no migration matches.

_delete() in compute/api was not using admin context, and was checking
for a false return from the DB call vs checking for an exception.

Added a test that covers both problems.

Fixes bug 1056601

Change-Id: Ib3c631dccbb2776761cf5acb8bab1d814bf3e282
(cherry picked from commit 8c9c380)

nova/compute/api.py

@@ -880,8 +880,12 @@ def _delete(self, context, instance):
             if instance['vm_state'] == vm_states.RESIZED:
                 # If in the middle of a resize, use confirm_resize to
                 # ensure the original instance is cleaned up too
-                migration_ref = self.db.migration_get_by_instance_and_status(
-                        context, instance['uuid'], 'finished')
+                get_migration = self.db.migration_get_by_instance_and_status
+                try:
+                    migration_ref = get_migration(context.elevated(),
+                            instance['uuid'], 'finished')
+                except exception.MigrationNotFoundByStatus:
+                    migration_ref = None
                 if migration_ref:
                     src_host = migration_ref['source_compute']
                     # Call since this can race with the terminate_instance.

nova/tests/compute/test_compute.py

@@ -2986,6 +2986,19 @@ def test_delete(self):
 
         db.instance_destroy(self.context, instance['uuid'])
 
+    def test_delete_in_resized(self):
+        instance, instance_uuid = self._run_instance(params={
+                'host': FLAGS.host})
+
+        instance['vm_state'] = vm_states.RESIZED
+
+        self.compute_api.delete(self.context, instance)
+
+        instance = db.instance_get_by_uuid(self.context, instance_uuid)
+        self.assertEqual(instance['task_state'], task_states.DELETING)
+
+        db.instance_destroy(self.context, instance['uuid'])
+
     def test_repeated_delete_quota(self):
         in_use = {'instances': 1}