At present, the CalibrationData API can't be used with test CalCat - you can point it to the right server, but the root directory it uses for constants is hardcoded. This MR allows passing in the root directory, e.g. /gpfs/exfel/d/cal_tst/caldb_store .
If no path is given, it uses the existing logic to find the default directory for the production calcat.
How Has This Been Tested?
TBD - it's a simple change, so I wanted to check if this is the design we want before getting into testing.
Types of changes
New feature (non-breaking change which adds functionality)
