Do not require driver_settings; use empty dict by default

sznqalibs/hoover.py

 # ## The Motor                                                             ## #
 # ########################################################################### #
 
-def regression_test(argsrc, tests, driver_settings, cleanup_hack=None,
+def regression_test(argsrc, tests, driver_settings=None, cleanup_hack=None,
                     apply_hacks=None, on_next=None):
     """Perform regression test with argsets from `argsrc`.
 
 
     on_next = on_next if on_next else lambda a, b: None
     apply_hacks = apply_hacks if apply_hacks else []
+    driver_settings = driver_settings if driver_settings else {}
 
     tracker = Tracker()
     last_argset = None