validate_collections_on_shutdown does not run validate on all databases, only the last one

for (let dbName of dbNames) {

    cmds.then("DEBUG: validating " + dbName, function(conn) {

        if (!validateCollections(conn.getDB(dbName), {full: true})) {

            return {shouldStop: true, reason: "collection validation failed"};

        }

    });

}