Add identity helper property to CellMapping

This adds CellMapping.identity, a property to help with quick logging of
a CellMapping. It's tempting to just log a a whole CellMapping object,
but that can be bad due to the credentials stored within. This adds a
convenient way to log the uuid or name-and-uuid of a CellMapping without
having to replicate the is-name-set-or-none logic everywhere.

Related to blueprint cells-aware-api
Change-Id: Ie8eaf08e9f5bda56431358c40ccf187251be4542

nova/objects/cell_mapping.py

@@ -32,6 +32,13 @@ class CellMapping(base.NovaTimestampObject, base.NovaObject):
         'database_connection': fields.StringField(),
         }
 
+    @property
+    def identity(self):
+        if 'name' in self and self.name:
+            return '%s(%s)' % (self.uuid, self.name)
+        else:
+            return self.uuid
+
     @staticmethod
     def _from_db_object(context, cell_mapping, db_cell_mapping):
         for key in cell_mapping.fields: