MDEV-5206: Incorrect slave old-style position in MDEV-4506, parallel replication.

In parallel replication, there are two kinds of events which are
executed in different ways.

Normal events that are part of event groups/transactions are executed
asynchroneously by being queued for a worker thread.

Other events like format description and rotate and such are executed
directly in the driver SQL thread.

If the direct execution of the other events were to update the old-style
position, then the position gets updated too far ahead, before the normal
events that have been queued for a worker thread have been executed. So
this patch adds some special cases to prevent such position updates ahead
of time, and instead queues dummy events for the worker threads, so that
they will at an appropriate time do the position updates instead.

(Also fix a race in a test case that happened to trigger while running
tests for this patch).

mysql-test/suite/rpl/t/rpl_parallel.test

@@ -92,6 +92,7 @@ INSERT INTO t2 VALUES (foo(10,
 
 --connection server_2
 FLUSH LOGS;
+--source include/wait_for_binlog_checkpoint.inc
 SET sql_log_bin=0;
 --delimiter ||
 CREATE FUNCTION foo(x INT, d1 VARCHAR(500), d2 VARCHAR(500))
@@ -148,6 +149,7 @@ SELECT * FROM t2 WHERE a >= 10 ORDER BY a;
 --let $binlog_file= slave-bin.000002
 --source include/show_binlog_events.inc
 FLUSH LOGS;
+--source include/wait_for_binlog_checkpoint.inc
 
 # Restart all the slave parallel worker threads, to clear all debug_sync actions.
 --connection server_2
@@ -161,6 +163,7 @@ SET debug_sync='RESET';
 --echo *** Test that group-committed transactions on the master can replicate in parallel on the slave. ***
 --connection server_1
 FLUSH LOGS;
+--source include/wait_for_binlog_checkpoint.inc
 CREATE TABLE t3 (a INT PRIMARY KEY, b INT) ENGINE=InnoDB;
 # Create some sentinel rows so that the rows inserted in parallel fall into
 # separate gaps and do not cause gap lock conflicts.