BUG#59147: rpl_circular_for_4_hosts fails sporadically

      
There is one part of the test case that needs to break
and re-establish the circular topology. For this the test
stops the slave threads on a couple of servers and restarts
them with START SLAVE. However, no check is done on the
status of the IO or SQL threads before proceeding with
the subsequent commands.
      
Because rpl_only_running_threads is set to 1 this can lead
to silently not syncing all slave threads as expected, 
ultimately resulting in unexpected results (and consequently
on a failing test run).
      
We fix this by replacing the START SLAVE instructions with
calls to --source include/start_slave.inc, which will wait
for the slave threads to be running (show 'Yes' in 
Slave_IO|SQL_Running fields of SHOW SLAVE STATUS) before 
proceeding. Additionally, we change rpl_sync.inc to make the
IO thread report that it is running when its running status
is any other than 'No'.

mysql-test/include/rpl_sync.inc

@@ -88,7 +88,7 @@ while ($_rpl_i) {
       {
         --echo Sync IO: $_rpl_slave_io_running; Sync SQL: $_rpl_slave_sql_running
       }
-      --let $_rpl_slave_io_running= `SELECT IF('$_rpl_slave_io_running' = 'Yes', 1, '')`
+      --let $_rpl_slave_io_running= `SELECT IF('$_rpl_slave_io_running' != 'No', 1, '')`
       --let $_rpl_slave_sql_running= `SELECT IF('$_rpl_slave_sql_running' = 'Yes', 1, '')`
       if ($_rpl_slave_io_running)
       {

mysql-test/suite/rpl/r/rpl_circular_for_4_hosts.result

@@ -121,11 +121,11 @@ Master D	12	D
 * Remove wrong event from C and restore B->C->D *
 include/stop_slave.inc
 DELETE FROM t1 WHERE a = 6;
-START SLAVE;
+include/start_slave.inc
 RESET MASTER;
 RESET SLAVE;
 include/rpl_change_topology.inc [new topology=1->2->3->4->1]
-START SLAVE;
+include/start_slave.inc
 include/rpl_sync.inc
 
 * Check data inserted before restoring schema A->B->C->D->A *

mysql-test/suite/rpl/t/rpl_circular_for_4_hosts.test

@@ -175,7 +175,7 @@ SELECT 'Master D',a,b FROM t1 WHERE c = 3 ORDER BY a,b;
 source include/stop_slave.inc;
 --connection server_3
 DELETE FROM t1 WHERE a = 6;
-START SLAVE;
+--source include/start_slave.inc
 --connection server_2
 --sync_slave_with_master server_3
 RESET MASTER;
@@ -189,7 +189,7 @@ RESET SLAVE;
 --source include/rpl_change_topology.inc
 #--replace_result $SERVER_MYPORT_3 SERVER_MYPORT_3 $file_d LOG_FILE $pos_d LOG_POS 
 #--eval CHANGE MASTER TO master_host='127.0.0.1',master_port=$SERVER_MYPORT_3,master_user='root',master_log_file='$file_d',master_log_pos=$pos_d
-START SLAVE;
+--source include/start_slave.inc
 --connection server_3
 --sync_slave_with_master server_4
 --source include/rpl_sync.inc