events in perfschema tests: use ON COMPLETION NOT PRESERVE

when the execution is very slow, under valgrind,
the event might manage to fire more than once, making the
test to fail

mysql-test/suite/perfschema/include/program_execution.inc

@@ -32,7 +32,7 @@ SET GLOBAL event_scheduler=ON;
 
 CREATE TABLE table_t(a INT);
 DELIMITER |;
-CREATE EVENT e1 ON SCHEDULE EVERY 2 SECOND DO
+CREATE EVENT e1 ON SCHEDULE EVERY 2 SECOND ON COMPLETION NOT PRESERVE DO
 BEGIN
   INSERT INTO table_t VALUES(1);
 END|