Ok, looks like the code for this has been committed to Common a long time ago. The change for the config hasn't come through somehow. There should be a similar change for MR.
As for putting this config thing into common: as much as it might seem suitable we can't do it because Common's part of Herriot doesn't have any config processing in it ;( In fact, I think we did a wrong thing when getHadoopLocalConfDir has been added to Common code. This has created indirect dependency to the config processing logic in upstream components (HDFS, MR).
Therefore, I think this patch (and its counterpart) can be committed to make the change complete for now. However, a new JIRA needs to be created to refactor this method away from the Common module.