Return of get_loaded_tables_for_scale_factor if hyrise failes

[Alexander-Dubrawski]

At the moment we are returning an empty list in hyrisecockpit.database_manager.job.get_loaded_tables.get_loaded_tables_for_scale_factor if the hyrise is failing.
It could be more meaningful to return None instead. So we can see that there are some unexpected problems with the hyrise. Every component that would use get_loaded_tables_for_scale_factor could handle this case differently and we would be more flexible.