mysql-test/innodb_trx_weight.inc: Add username root to the "connect" statement.

The Unix user running mysql-test-run usually does not have any privileges
on the MySQL test database.

mysql-test/innodb_trx_weight.inc

--- connect (con1,localhost,,,)
--- connect (con2,localhost,,,)
+-- connect (con1,localhost,root,,)
+-- connect (con2,localhost,root,,)
 
 -- connection con1
 SET autocommit=0;