Bug #28991: rpl_events failure in pushbuild

In tests waiting on a timeout is not deterministic enough
to make sure that an event actually finished executing.
Fixed the test by waiting in a loop and checking the effect
that the event is supposed to produce.

mysql-test/include/rpl_events.inc

@@ -29,6 +29,9 @@ SELECT db, name, status, originator FROM mysql.event WHERE db = 'test' AND name
 
 # wait 3 seconds, so the event can trigger
 --real_sleep 3
+let $wait_condition= 
+  SELECT count(*) = 1 FROM t1 WHERE c = 'from justonce';
+--source include/wait_condition.inc  
 
 # check that table t1 contains something
 --echo "in the master"