arg_validator: make ArgValidatorDeprecated a subclass of ArgValidator
arg_validator: make ArgValidatorDeprecated a subclass of ArgValidator

ArgValidatorDeprecated is used as a nested validator, it also should
subtype ArgValidator base class. Technially, in python you can do duck
typing and get away with a different class that merely behaves
sufficiently similar. But why?

That way, we also can set default_value=ArgValidator.MISSING.
As a result, we no longer need to special case ArgValidatorDeprecated
at various places, because the default value will indicate that
it should not be present.

Co-authored-by: Till Maas <opensource@till.name>

Signed-off-by: Thomas Haller <16e26612e4159990a6b3691e92592e691ff74132@redhat.com>

linux-system-roles/network,linux-system-roles/network,linux-system-roles/network