MDEV-12764 main.log_tables-big fails in buildbot due to connect_log

Additionally internal check was failing because the test did not
restore a global value properly

mysql-test/r/log_tables-big.result

 set @@global.log_output = 'TABLE';
+connect  con1,localhost,root,,;
+connect  con2,localhost,root,,;
+connection con1;
 set session long_query_time=10;
 select get_lock('bug27638', 1);
 get_lock('bug27638', 1)
 1
+connection con2;
 set session long_query_time=1;
 select get_lock('bug27638', 2);
 get_lock('bug27638', 2)
@@ -25,7 +29,11 @@ select if (query_time >= '00:01:40', 'OK', 'WRONG') as qt, sql_text from mysql.s
 where sql_text = 'select get_lock(\'bug27638\', 101)';
 qt	sql_text
 OK	select get_lock('bug27638', 101)
+connection con1;
 select release_lock('bug27638');
 release_lock('bug27638')
 1
+connection default;
+disconnect con1;
+disconnect con2;
 set @@global.log_output=default;

mysql-test/t/log_tables-big-master.opt

---log-output=table,file --slow-query-log --general-log --general-log-file="" --slow-query-log-file=""
+--slow-query-log --general-log --general-log-file="" --slow-query-log-file=""