createMETS2: prefix PREMIS elements

Leaving PREMIS elements unprefixed resulted in any other unprefixed
elements being interpreted as being PREMIS - for example, un-namespaced
documents from external sources.

Fixes #7055.
Print exception message instead of sys.exc_info
Metadata processing: Add file ID, characterization

refs #6575

Metadata files should have identification and characterization information
in the METS file. Add those microservices to metadata processing. Update
processing config to reflect this. Fix a couple microservice group
discontinuities.