The finalize step is now always separate from processing, and we rely on
Slurm's dependency system to ensure it runs after they finish. So we
don't need to wait for them to finish.

FIX - Recreate folder if sphinx-rep already existed and fix warning message for concurrency parameter.

It was just a warning for summary.rst, but might as well.

This metadata file subsumes the old retrieved constants YAML file.  The commit includes some refactoring centered around pathlib.