MDEV-6720 - enable connection log in mysqltest by default

This is an addition to original patch. Removed meaningless
"echo SET SESSION AUTOCOMMIT=0" (transaction is started explicitely on
master anyway).

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

@@ -116,7 +116,6 @@ include/wait_for_slave_sql_to_start.inc
 # SAVEPOINT and ROLLBACK TO have the same problem in BUG#43263
 # This was reported by BUG#50407
 connection master;
-SET SESSION AUTOCOMMIT=0
 BEGIN;
 INSERT INTO db1.t1 VALUES(20);
 # 
@@ -164,7 +163,6 @@ master-bin.000001	#	Query	#	#	use `db1`; INSERT INTO db1.t2 VALUES("after rollba
 master-bin.000001	#	Query	#	#	use `db1`; INSERT INTO db1.t1 VALUES(50)
 master-bin.000001	#	Xid	#	#	COMMIT /* XID */
 connection slave;
-[on slave]
 #
 # Verify INSERT statements in savepoints are executed, for MyISAM table
 # is not effected by ROLLBACK TO

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

@@ -129,7 +129,6 @@ source include/wait_for_slave_sql_to_start.inc;
 --echo # SAVEPOINT and ROLLBACK TO have the same problem in BUG#43263
 --echo # This was reported by BUG#50407
 connection master;
-echo SET SESSION AUTOCOMMIT=0;
 let $binlog_start=query_get_value(SHOW MASTER STATUS, Position, 1);
 
 BEGIN;
@@ -157,7 +156,6 @@ COMMIT;
 source include/show_binlog_events.inc;
 sync_slave_with_master;
 
---echo [on slave]
 --echo #
 --echo # Verify INSERT statements in savepoints are executed, for MyISAM table
 --echo # is not effected by ROLLBACK TO