Implement catalogue createDiskSystem,
getAllDiskSystems, deleteDiskSystem methods.

The implemantation currently returns an empty disk system.

Turns out that properly splitting the query with a "persistent"
temp table is ~2x faster than the full query.

cta-fst-gc now logs an error if it cannot list the contents of an FST filesystem or if determine the filesystem's sub directories

ctafstgcd.py no longer logs an ERROR when it fails to stat() a file that has been deleted by the FST