main.wait_timeout failed in buildbot with Lost connection to MySQL server during query

main.wait_timeout                        w4 [ fail ]

        Test ended at 2019-03-14 09:15:42

CURRENT_TEST: main.wait_timeout

mysqltest: At line 132: query 'SET @@global.wait_timeout= $start_value' failed: 2013: Lost connection to MySQL server during query

The result from queries just before the failure was:

< snip >

3

disconnection default;

connection wait_con;

connection con1;

--disable_reconnect;

SELECT 1;

1

1

connection wait_con;

connection con1;

SELECT 2;

Got one of the listed errors

--enable_reconnect;

SELECT 3;

3

3

SET @@global.wait_timeout= <start_value>;