MDEV-20138 innodb.trx_id_future fails on 10.3+

Starting with MDEV-12288 in MariaDB Server 10.3,
the transaction identifiers on records will be reset on purge.
Because purge might or might not run to completion before shutdown,
it could happen that the bogus transaction identifier that our
test is writing will be reset by purge after restart, and the
expected warning message on SELECT will fail to appear.

We resolve the race condition by ensuring that purge runs to
completion before the shutdown.

mysql-test/suite/innodb/r/trx_id_future.result

@@ -2,8 +2,10 @@
 # Bug #20445525	ADD A CONSISTENCY CHECK AGAINST DB_TRX_ID BEING
 #		IN THE FUTURE
 #
+SET GLOBAL innodb_purge_rseg_truncate_frequency=1;
 CREATE TABLE t1(a INT) row_format=redundant engine=innoDB;
 INSERT INTO t1 VALUES(1);
+InnoDB		0 transactions not purged
 NOT FOUND /\[Warning\] InnoDB: A transaction id in a record of table `test`\.`t1` is newer than the system-wide maximum/ in mysqld.1.err
 call mtr.add_suppression("\\[Warning\\] InnoDB: A transaction id in a record of table `test`\\.`t1` is newer than the system-wide maximum");
 SELECT * FROM t1;

mysql-test/suite/innodb/t/trx_id_future.test

@@ -7,13 +7,14 @@
 --source include/have_innodb.inc
 --source include/not_embedded.inc
 
+SET GLOBAL innodb_purge_rseg_truncate_frequency=1;
 let PAGE_SIZE=`select @@innodb_page_size`;
 
 CREATE TABLE t1(a INT) row_format=redundant engine=innoDB;
 INSERT INTO t1 VALUES(1);
 
 let MYSQLD_DATADIR=`select @@datadir`;
-
+--source include/wait_all_purged.inc
 --source include/shutdown_mysqld.inc
 
 perl;