[AIRFLOW-2574] Cope with '%' in SQLA DSN when running migrations (#3787)
[AIRFLOW-2574] Cope with '%' in SQLA DSN when running migrations (#3787)

Alembic uses a ConfigParser like Airflow does, and "%% is a special
value in there, so we need to escape it. As per the Alembic docs:

> Note that this value is passed to ConfigParser.set, which supports
> variable interpolation using pyformat (e.g. `%(some_value)s`). A raw
> percent sign not part of an interpolation symbol must therefore be
> escaped, e.g. `%%`
owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow