sporadic failures of rpl.rpl_rewrite_db_sys_vars

first stop the slave, then run commands on the master that are
supposed to fail on the slave, then start the slave.

if you swap first two steps, the slave might get and execute those
commands before it's stopped, which will fail the test.

also, improve debugability

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

@@ -12,11 +12,9 @@ select @@session.server_id;
 create database replica_db1;
 create database y;
 create database test_replica;
-SELECT @@GLOBAL.replicate_rewrite_db;
-@@GLOBAL.replicate_rewrite_db
-primary_db1->replica_db1,x->y
-# Ensuring SHOW SLAVE STATUS produces correct value for Replicate_Rewrite_DB...
-# ...success
+SELECT @@GLOBAL.replicate_rewrite_db, 'primary_db1->replica_db1,x->y' as 'Replicate_Rewrite_DB from SHOW SLAVE STATUS';
+@@GLOBAL.replicate_rewrite_db	Replicate_Rewrite_DB from SHOW SLAVE STATUS
+primary_db1->replica_db1,x->y	primary_db1->replica_db1,x->y
 # Create DBs and tables on primary
 connection master;
 create database primary_db1;
@@ -60,15 +58,13 @@ SELECT @@GLOBAL.replicate_rewrite_db;
 @@GLOBAL.replicate_rewrite_db
 primary_db1->replica_db1,x->y
 SET @@GLOBAL.replicate_rewrite_db="test_master->test_replica";
-SELECT @@GLOBAL.replicate_rewrite_db;
-@@GLOBAL.replicate_rewrite_db
-test_master->test_replica
 SHOW DATABASES like 'test_replica';
 Database (test_replica)
 test_replica
 include/start_slave.inc
-# Ensuring SHOW SLAVE STATUS produces correct value for Replicate_Rewrite_DB...
-# ...success
+SELECT @@GLOBAL.replicate_rewrite_db, 'test_master->test_replica' as 'Replicate_Rewrite_DB from SHOW SLAVE STATUS';
+@@GLOBAL.replicate_rewrite_db	Replicate_Rewrite_DB from SHOW SLAVE STATUS
+test_master->test_replica	test_master->test_replica
 # Create DB and tables on primary
 connection master;
 create database test_master;
@@ -94,6 +90,8 @@ t
 3
 include/diff_tables.inc [master:test_master.my_table,slave:test_replica.my_table]
 # Update of values on primary for DB not set in replication_rewrite_db
+include/stop_slave.inc
+include/reset_slave.inc
 connection master;
 use x;
 insert into my_table values (314);
@@ -104,8 +102,6 @@ t
 314
 include/save_master_gtid.inc
 connection slave;
-include/stop_slave.inc
-include/reset_slave.inc
 include/start_slave.inc
 SELECT @@GLOBAL.replicate_rewrite_db;
 @@GLOBAL.replicate_rewrite_db

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

@@ -19,15 +19,8 @@ create database replica_db1;
 create database y;
 # This DB will be rewrited from test case
 create database test_replica;
-SELECT @@GLOBAL.replicate_rewrite_db;
 let $rewrite_db_sss= query_get_value(SHOW SLAVE STATUS, Replicate_Rewrite_DB, 1);
---echo # Ensuring SHOW SLAVE STATUS produces correct value for Replicate_Rewrite_DB...
-if (`SELECT strcmp(@@global.replicate_rewrite_db, "$rewrite_db_sss") != 0`)
-{
-    die SHOW SLAVE STATUS Replicate_Rewrite_DB value $rewrite_db_sss does not match variable @@GLOBAL.replicate_rewrite_db;
-}
---echo # ...success
-
+eval SELECT @@GLOBAL.replicate_rewrite_db, '$rewrite_db_sss' as 'Replicate_Rewrite_DB from SHOW SLAVE STATUS';
 
 --echo # Create DBs and tables on primary
 connection master;
@@ -63,16 +56,10 @@ source include/stop_slave.inc;
 SET @save_replicate_rewrite_db = @@GLOBAL.replicate_rewrite_db;
 SELECT @@GLOBAL.replicate_rewrite_db;
 SET @@GLOBAL.replicate_rewrite_db="test_master->test_replica";
-SELECT @@GLOBAL.replicate_rewrite_db;
 SHOW DATABASES like 'test_replica';
 source include/start_slave.inc;
 let $rewrite_db_sss= query_get_value(SHOW SLAVE STATUS, Replicate_Rewrite_DB, 1);
---echo # Ensuring SHOW SLAVE STATUS produces correct value for Replicate_Rewrite_DB...
-if (`SELECT strcmp(@@global.replicate_rewrite_db, "$rewrite_db_sss") != 0`)
-{
-    die SHOW SLAVE STATUS Replicate_Rewrite_DB value $rewrite_db_sss does not match variable @@GLOBAL.replicate_rewrite_db;
-}
---echo # ...success
+eval SELECT @@GLOBAL.replicate_rewrite_db, '$rewrite_db_sss' as 'Replicate_Rewrite_DB from SHOW SLAVE STATUS';
 
 --echo # Create DB and tables on primary
 connection master;
@@ -101,6 +88,9 @@ select * from test_replica.my_table;
 --source include/diff_tables.inc
 
 --echo # Update of values on primary for DB not set in replication_rewrite_db
+--source include/stop_slave.inc
+--source include/reset_slave.inc
+
 connection master;
 use x;
 insert into my_table values (314);
@@ -108,9 +98,6 @@ select * from my_table;
 --source include/save_master_gtid.inc
 
 connection slave;
---let $rpl_only_running_threads=1
---source include/stop_slave.inc
---source include/reset_slave.inc
 --source include/start_slave.inc
 SELECT @@GLOBAL.replicate_rewrite_db;
 --source include/sync_with_master_gtid.inc