Ability to read deleted system metadata records.

Update _instance_system_metadata_get_query to use read_deleted from
the passed in context instead of just hard-coding "no". Also, use
this to ensure system metadata is always collected during delete,
even if the instance was deleted elsewhere.

Fixes bug 1019357

Change-Id: I9285f110801435344fcaa76ba21fb88c23aac2fa

nova/compute/manager.py

@@ -761,12 +761,10 @@ class ComputeManager(manager.SchedulerDependentManager):
                                          vm_state=vm_states.DELETED,
                                          task_state=None,
                                          terminated_at=timeutils.utcnow())
-        # Pull the system_metadata before we delete the instance, so we
-        # can pass it to delete.end notification, as it will not be able
-        # to look it up anymore, if it needs it.
-        system_meta = self.db.instance_system_metadata_get(context,
-                instance_uuid)
         self.db.instance_destroy(context, instance_uuid)
+        with utils.temporary_mutation(context, read_deleted="yes"):
+            system_meta = self.db.instance_system_metadata_get(context,
+                instance_uuid)
         self._notify_about_instance_usage(context, instance, "delete.end",
                 system_metadata=system_meta)
 

nova/db/sqlalchemy/api.py

@@ -4240,8 +4240,8 @@ def instance_metadata_update(context, instance_uuid, metadata, delete):
 # System-owned metadata
 
 def _instance_system_metadata_get_query(context, instance_uuid, session=None):
-    return model_query(context, models.InstanceSystemMetadata, session=session,
-                       read_deleted="no").\
+    return model_query(context, models.InstanceSystemMetadata,
+                       session=session).\
                     filter_by(instance_uuid=instance_uuid)