Fixed random failure in main.kill_processlist-6619

The problem was that SHOW PROCESSLIST was done before the command of
the default connection was cleared.

Reviewer: Sergei Golubchik <serg@mariadb.org>

mysql-test/main/kill_processlist-6619.result

+SET DEBUG_SYNC='dispatch_command_end SIGNAL ready WAIT_FOR go';
+select 1;
 connect  con1,localhost,root,,;
+SET DEBUG_SYNC='now wait_for ready';
+SET DEBUG_SYNC='now signal go';
 SHOW PROCESSLIST;
 Id	User	Host	db	Command	Time	State	Info	Progress
 #	root	#	test	Sleep	#	#	NULL	0.000
@@ -6,6 +10,8 @@ Id	User	Host	db	Command	Time	State	Info	Progress
 SET DEBUG_SYNC='before_execute_sql_command SIGNAL ready WAIT_FOR go';
 SHOW PROCESSLIST;
 connection default;
+1
+1
 SET DEBUG_SYNC='now WAIT_FOR ready';
 KILL QUERY con_id;
 SET DEBUG_SYNC='now SIGNAL go';

mysql-test/main/kill_processlist-6619.test

@@ -4,7 +4,14 @@
 --source include/not_embedded.inc
 --source include/have_debug_sync.inc
 
+# This is to ensure that the following SHOW PROCESSLIST does not show the query
+SET DEBUG_SYNC='dispatch_command_end SIGNAL ready WAIT_FOR go';
+--send select 1
+
 --connect (con1,localhost,root,,)
+SET DEBUG_SYNC='now wait_for ready';
+SET DEBUG_SYNC='now signal go';
+
 --let $con_id = `SELECT CONNECTION_ID()`
 --replace_result Execute Query
 --replace_column 1 # 3 # 6 # 7 #
@@ -12,6 +19,8 @@ SHOW PROCESSLIST;
 SET DEBUG_SYNC='before_execute_sql_command SIGNAL ready WAIT_FOR go';
 send SHOW PROCESSLIST;
 --connection default
+--reap
+
 # We must wait for the SHOW PROCESSLIST query to have started before sending
 # the kill. Otherwise, the KILL may be lost since it is reset at the start of
 # query execution.