Dataone-indexer can handle legacy Metacat object repository

[taojing2002]

In the ticket of Integrate Dataone-indexer to Dataone CN #189 , we will deploy dataone-indexer without upgrading the Metacat instance to version 3.*. This requires dataone-indexer can handle the legacy Metacat object repository, i.e. /var/metacat/data and /var/metacat/documents.

Dataone-Indexer 3.0 had the feature. But we have eliminated it since 3.1* to only handle the new object repository - hashstore. We need to restore the feature. So the new version can handle both hashstore and the legacy object repository.