MDEV-12179: Per-engine mysql.gtid_slave_pos table

Intermediate commit.

Make test case tolerant to an earlier test case changing the storage
engine for mysql.gtid_slave_pos.

mysql-test/suite/rpl/r/rpl_mdev12179.result

@@ -48,6 +48,7 @@ a
 1
 include/stop_slave.inc
 SET sql_log_bin=0;
+ALTER TABLE mysql.gtid_slave_pos ENGINE=MyISAM;
 CREATE TABLE mysql.gtid_slave_pos_innodb LIKE mysql.gtid_slave_pos;
 ALTER TABLE mysql.gtid_slave_pos_innodb ENGINE=InnoDB;
 INSERT INTO mysql.gtid_slave_pos_innodb SELECT * FROM mysql.gtid_slave_pos;

mysql-test/suite/rpl/t/rpl_mdev12179.test

@@ -40,6 +40,9 @@ SELECT * FROM t1 ORDER BY a;
 SELECT * FROM t1 ORDER BY a;
 --source include/stop_slave.inc
 SET sql_log_bin=0;
+# Reset storage engine for mysql.gtid_slave_pos in case an earlier test
+# might have changed it to InnoDB.
+ALTER TABLE mysql.gtid_slave_pos ENGINE=MyISAM;
 CREATE TABLE mysql.gtid_slave_pos_innodb LIKE mysql.gtid_slave_pos;
 ALTER TABLE mysql.gtid_slave_pos_innodb ENGINE=InnoDB;
 INSERT INTO mysql.gtid_slave_pos_innodb SELECT * FROM mysql.gtid_slave_pos;