This bug is a side-effect of fix for MDEV-6924, where we completely
stopped a statement-based event from getting into the binlog cache when
binary logging is not enabled (and thus, wsrep_emulate_binlog mode = 1).
As a result, the SBR events were not replicated.

Fixed by allowing the SBR events to be written into the binlog cache.

Note: Only DMLs were affected as DDLs are replicated via TOI.

Merged galera_create_trigger.test from github.com/codership/mysql-wsrep.