MDEV-7431 main.log_tables fails sporadically in buildbot

  
Structure of the table created by the test to archive mysql.slow_log
data didn't match the structure of mysql.slow_log. The failure only 
appeared if the slow_log was not empty, which was very rare. 
  
Updated the structure of the table. 

mysql-test/r/log_tables.result

@@ -536,7 +536,8 @@ CREATE TABLE `db_17876.slow_log_data` (
 `last_insert_id` int(11) default NULL,
 `insert_id` int(11) default NULL,
 `server_id` int(11) default NULL,
-`sql_text` mediumtext 
+`sql_text` mediumtext,
+`thread_id` bigint(21) unsigned default NULL
 );
 CREATE TABLE `db_17876.general_log_data` (
 `event_time` timestamp(6) NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,

mysql-test/t/log_tables.test

@@ -727,7 +727,8 @@ CREATE TABLE `db_17876.slow_log_data` (
   `last_insert_id` int(11) default NULL,
   `insert_id` int(11) default NULL,
   `server_id` int(11) default NULL,
-  `sql_text` mediumtext 
+  `sql_text` mediumtext,
+  `thread_id` bigint(21) unsigned default NULL
 );
 
 CREATE TABLE `db_17876.general_log_data` (