Merge pull request #698 from matrix-org/erikj/port_script_fix

scripts/synapse_port_db

synapse/app/homeserver.py

synapse/storage/engines/__init__.py

synapse/storage/engines/postgres.py

synapse/storage/engines/sqlite3.py

synapse/storage/prepare_database.py

synapse/storage/schema/delta/14/upgrade_appservice_db.py

synapse/storage/schema/delta/20/pushers.py

synapse/storage/schema/delta/25/fts.py

synapse/storage/schema/delta/27/ts.py

synapse/storage/schema/delta/30/as_users.py

tests/storage/test_base.py

tests/utils.py