rpl.rpl_truncate_3innodb failed in buildbot with syntax error in test

rpl.rpl_truncate_3innodb 'mix,xtradb'    w4 [ fail ]

        Test ended at 2019-05-09 13:17:08

CURRENT_TEST: rpl.rpl_truncate_3innodb

mysqltest: In included file "./include/show_rpl_debug_info.inc": 

included from ./include/wait_for_slave_param.inc at line 115:

included from ./include/wait_for_slave_io_to_start.inc at line 40:

included from ./include/wait_for_slave_to_start.inc at line 26:

included from ./include/start_slave.inc at line 35:

included from ./include/rpl_for_each_slave.inc at line 33:

included from ./include/rpl_start_slaves.inc at line 30:

included from ./include/rpl_init.inc at line 210:

included from ./include/master-slave.inc at line 38:

included from ./extra/rpl_tests/rpl_truncate.test at line 6:

included from /usr/share/mysql/mysql-test/suite/rpl/t/rpl_truncate_3innodb.test at line 4:

At line 93: Found line beginning with --  that didn't contain a valid mysqltest command, check your syntax or use # if you intended to write a comment

The result from queries just before the failure was:

include/master-slave.inc

 - saving '/dev/shm/var/4/log/rpl.rpl_truncate_3innodb-mix,xtradb/' to '/dev/shm/var/log/rpl.rpl_truncate_3innodb-mix,xtradb/'

Retrying test rpl.rpl_truncate_3innodb, attempt(2/3)...

worker[4] > Restart  - not started

worker[4] > Restart  - not started

rpl.rpl_truncate_3innodb 'mix,xtradb'    w4 [ retry-pass ]    964