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-google/certbot_dns_google/dns_google.py

@@ -274,7 +274,7 @@ class _GoogleClient(object):
                 raise errors.PluginError('Encountered error finding managed zone: {0}'
                                          .format(e))
 
-            if len(zones) > 0:
+            if zones:
                 zone_id = zones[0]['id']
                 logger.debug('Found id of %s for %s using name %s', zone_id, domain, zone_name)
                 return zone_id
@@ -303,5 +303,4 @@ class _GoogleClient(object):
 
         if isinstance(content, bytes):
             return content.decode()
-        else:
-            return content
+        return content