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-dns-cloudflare/certbot_dns_cloudflare/dns_cloudflare.py

@@ -159,7 +159,7 @@ class _CloudflareClient(object):
                                          'you have supplied valid Cloudflare API credentials.{2}'
                                          .format(code, e, ' ({0})'.format(hint) if hint else ''))
 
-            if len(zones) > 0:
+            if zones:
                 zone_id = zones[0]['id']
                 logger.debug('Found zone_id of %s for %s using name %s', zone_id, domain, zone_name)
                 return zone_id
@@ -191,9 +191,9 @@ class _CloudflareClient(object):
             logger.debug('Encountered CloudFlareAPIError getting TXT record_id: %s', e)
             records = []
 
-        if len(records) > 0:
+        if records:
             # Cleanup is returning the system to the state we found it. If, for some reason,
             # there are multiple matching records, we only delete one because we only added one.
             return records[0]['id']
-        else:
-            logger.debug('Unable to find TXT record.')
+        logger.debug('Unable to find TXT record.')
+        return None