Bug#31167 Introduction of @@hostname breaks replication in a ring

- Use a local uservariable to avoid @@hostname in binlog


scripts/mysql_system_tables_data.sql:
  Load @@hostname into a local user variable to avoid
  writing @@hostname to the binary log that potentially
  would be replicated to a slave server that not yet was upgraded
  to have @@hostname.

scripts/mysql_system_tables_data.sql

@@ -15,7 +15,8 @@ DROP TABLE tmp_db;
 -- from local machine if "users" table didn't exist before
 CREATE TEMPORARY TABLE tmp_user LIKE user;
 INSERT INTO tmp_user VALUES ('localhost','root','','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','','','','',0,0,0,0);
-REPLACE INTO tmp_user VALUES (@@hostname,'root','','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','','','','',0,0,0,0);
+set @hostname= @@hostname;
+REPLACE INTO tmp_user VALUES (@hostname,'root','','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','','','','',0,0,0,0);
 REPLACE INTO tmp_user VALUES ('127.0.0.1','root','','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','','','','',0,0,0,0);
 INSERT INTO user SELECT * FROM tmp_user WHERE @had_user_table=0;
 DROP TABLE tmp_user;