perfschema.threads_mysql sporadic failures

wait a bit more thoroughly for event scheduler to be fully started

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

-# threads are removed from:
+# threads are added to:
 # - information_schema.processlist
 # - performance_schema.threads
 # at different times, so we may have to wait a little more
-# for the event_scheduler to shutdown
+# for the event_scheduler to start
 #
 let $wait_condition=
   SELECT COUNT(*) = 1 FROM performance_schema.threads
-  WHERE name like 'thread/sql/event%';
+  WHERE name LIKE 'thread/sql/event%' AND processlist_command IS NOT NULL;
 --source include/wait_condition.inc