MTR: Write a record when change_user command is executed

CREATE USER foo;

--connect (con1,localhost,root,,)

SELECT CURRENT_USER();

--change_user foo

SELECT CURRENT_USER();

--disconnect con1

--connection default

DROP USER foo;

CREATE USER foo;

connect  con1,localhost,root,,;

SELECT CURRENT_USER();

CURRENT_USER()

root@localhost

<-- HERE we should have the extra record-->

SELECT CURRENT_USER();

CURRENT_USER()

foo@%

disconnect con1;

connection default;

DROP USER foo;