Fix Pylint upgrade issues

* Remove unsupported pylint disable options
    * star-args removed in Pylint 1.4.3
    * abstract-class-little-used removed in Pylint 1.4.3

* Fixes new lint errors

* Copy dummy-variable-rgx expression to new ignored-argument-names expression to ignore unused funtion arguments

* Notable changes
    * Refactor to satisfy Pylint no-else-return warning
    * Fix Pylint inconsistent-return-statements warning
    * Refactor to satisfy consider-iterating-dictionary
    * Remove methods with only super call to satisfy useless-super-delegation
    * Refactor too-many-nested-statements where possible
    * Suppress type checked errors where member is dynamically added (notably derived from josepy.JSONObjectWithFields)
    * Remove None default of func parameter for ExitHandler and ErrorHandler

Resolves #5973

certbot/plugins/selection.py

@@ -82,8 +82,7 @@ def pick_plugin(config, default, plugins, question, ifaces):
         plugin_ep = choose_plugin(list(six.itervalues(prepared)), question)
         if plugin_ep is None:
             return None
-        else:
-            return plugin_ep.init()
+        return plugin_ep.init()
     elif len(prepared) == 1:
         plugin_ep = list(prepared.values())[0]
         logger.debug("Single candidate plugin: %s", plugin_ep)