Fix flake8 warnings for new flake8

setup.cfg

synapse/api/auth.py

synapse/app/__init__.py

synapse/app/homeserver.py

synapse/appservice/api.py

synapse/federation/federation_client.py

synapse/handlers/_base.py

synapse/handlers/directory.py

synapse/handlers/events.py

synapse/handlers/presence.py

synapse/handlers/register.py

synapse/handlers/room.py

synapse/http/matrixfederationclient.py

synapse/notifier.py

synapse/push/push_rule_evaluator.py

synapse/rest/client/v1/login.py

synapse/rest/client/v1/pusher.py

synapse/rest/client/v1/register.py

synapse/rest/client/v2_alpha/register.py

synapse/rest/client/versions.py