SERVER-42978 changed the validate cmd's error message for NamespaceNotFound from 'ns not found' to "Collection 'test1_fsmdb0.tmpLhDxo.convertToCapped.convert_to_capped_collection_6' does not exist to validate." (for example).

The testing hook running validate cmds, however, filters out by error msg, however, here. which is broken because the error msg changed in SERVER-42978.