MDEV-11675. rpl_start_alter_ftwrl.test is refined

The test could fail sporadically because of not anticipated
race on slave between CREATE and ALTER queries.

Fixed to synchronize slave and master wrt CREATE.

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

@@ -10,6 +10,10 @@ include/start_slave.inc
 connection master;
 SET @@session.binlog_alter_two_phase=true;
 CREATE TABLE t1 (a INT) ENGINE=innodb;
+include/save_master_gtid.inc
+connection slave;
+include/sync_with_master_gtid.inc
+connection master;
 SET @@session.alter_algorithm='INSTANT';
 SET @@session.gtid_domain_id=11;
 ALTER TABLE t1 ADD COLUMN b int;

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

@@ -26,7 +26,13 @@ SET @@global.debug_dbug="+d,at_write_start_alter";
 SET @@session.binlog_alter_two_phase=true;
 
 CREATE TABLE t1 (a INT) ENGINE=innodb;
+--source include/save_master_gtid.inc
 
+# Make sure the table exists on slave now.
+--connection slave
+--source include/sync_with_master_gtid.inc
+
+--connection master
 SET @@session.alter_algorithm='INSTANT';
 SET @@session.gtid_domain_id=11;
 ALTER TABLE t1 ADD COLUMN b int;