Support metadata files added during Ingest

refs #6488

When writing the METS, check for a metadata.csv added to the SIP, in
addition to ones from the originating transfers.  Add conversion of
metadata.json to metadata.csv for files added during ingest.
Hack to allow reingest on same pipeline

refs #6488

Temporary hack to allow reingest on the same pipeline for testing.  Assumes
that everything necessary is still in the DB from initial processing.