Fix a race

Wait at the end of the test for all events to finish.
Then continue to the next result. This should be done, as the
server won't be restarted, and although events are dropped with
drop database, they could still be executing in memory.


mysql-test/r/events_restart_phase3.result:
  fix result
mysql-test/t/events_restart_phase3.test:
  Fix a race
  Wait at the end of the test for all events to finish.
  Then continue to the next result. This should be done, as the
  server won't be restarted, and although events are dropped with
  drop database, they could still be executing in memory.