galera.galera_wsrep_log_conficts failed in buildbot upon before testcase check

galera.galera_wsrep_log_conficts 'xtradb' w4 [ fail ]

        Test ended at 2017-09-07 07:25:26

CURRENT_TEST: galera.galera_wsrep_log_conficts

Could not execute 'check-testcase' before testcase 'galera.galera_wsrep_log_conficts' (res: 1):

mysqltest: Logging to '/dev/shm/var/4/tmp/check-mysqld_2.log'.

mysqltest: Results saved in '/dev/shm/var/4/tmp/check-mysqld_2.result'.

mysqltest: Connecting to server localhost:16041 (socket /dev/shm/var/tmp/4/mysqld.2.sock) as 'root', connection 'default', attempt 0 ...

mysqltest: ... Connected.

mysqltest: Start processing test commands from './include/check-testcase.test' ...

mysqltest: At line 78: query 'call mtr.check_testcase()' failed: 1047: WSREP has not yet prepared node for application use

not ok

mysqltest failed but provided no output