Reingest: Only store first and last METS
Reingest: Only store first and last METS

When storing a reingested AIP, keep the backup METS if there isn't one
already.  This should keep the original AIP METS, and the most recently
updated METS.

artefactual/archivematica-storage-service,artefactual/archivematica-storage-service,artefactual/archivematica-storage-service,artefactual/archivematica-storage-service