Fix accumulation of old rows in mysql.gtid_slave_pos

This would happen especially in optimistic parallel replication, where there
is a good chance that a transaction will be rolled back (due to conflicts)
after it has executed record_gtid(). If the transaction did any deletions of
old rows as part of record_gtid(), those deletions will be undone as well.
And the code did not properly ensure that the deletions would be re-tried.

This patch makes record_gtid() remember the list of deletions done as part
of a transaction. Then in rpl_slave_state::update() when the changes have
been committed, we discard the list. However, in case of error and rollback,
in cleanup_context() we will instead put the list back into
rpl_global_gtid_slave_state so that the deletions will be re-tried later.

Probably fixes part of the cause of MDEV-12147 as well.

Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>

mysql-test/suite/rpl/r/rpl_parallel_optimistic.result

@@ -571,4 +571,10 @@ SET GLOBAL slave_parallel_mode=@old_parallel_mode;
 SET GLOBAL slave_parallel_threads=@old_parallel_threads;
 include/start_slave.inc
 DROP TABLE t1, t2, t3;
+include/save_master_gtid.inc
+include/sync_with_master_gtid.inc
+Check that no more than the expected last two GTIDs are in mysql.gtid_slave_pos
+select count(*) from mysql.gtid_slave_pos order by domain_id, sub_id;
+count(*)
+2
 include/rpl_end.inc