Fix removed pywikibot config property db_hostname

https://phabricator.wikimedia.org/rPWBC2d73643f70a3f3289ff83e7ec142727d79d2649c

lib/mysqlred.py

@@ -49,7 +49,7 @@ Base = declarative_base()
 url = URL( "mysql+pymysql",
            username=config.db_username,
            password=config.db_password,
-           host=config.db_hostname,
+           host=config.db_hostname_format.format('tools'),
            port=config.db_port,
            database=( config.db_username +
                       jogobot.config['redundances']['db_suffix'] ),