tidy: misc.Action_Exit: figure out and fix __call__()

[reidpr]

Split from #1860. Pylint: W0223 abstract-method

charliecloud/lib/misc.py

Lines 20 to 23 in 5ceefa7

	class Action_Exit(argparse.Action):
	def __init__(self, *args, **kwargs):
	super().__init__(nargs=0, *args, **kwargs)

Complaint:

Method __call__ is abstract in class Action but is not overridden in child class Action_Exit