Make workers work on Py3 (#4027)

changelog.d/4027.bugfix

synapse/app/_base.py

synapse/app/event_creator.py

synapse/app/pusher.py

synapse/app/synchrotron.py

synapse/python_dependencies.py

synapse/replication/slave/storage/_base.py

synapse/replication/slave/storage/deviceinbox.py

synapse/replication/slave/storage/devices.py

synapse/replication/slave/storage/groups.py

synapse/replication/slave/storage/keys.py

synapse/replication/slave/storage/presence.py

synctl