password was changed and implement password rotation

We need to track when the password was last changed 
and implement password rotation.

Put a TIMESTAMP column inside mysql.user table and 
update it when the password is updated.

Put another column in mysql.user, holding the number
of days after which the password must expire.

Introduce extension of query ALTER USER as:

ALTER USER foo PASSWORD EXPIRE EVERY <day> DAY;
ALTER USER foo PASSWORD EXPIRE NEVER;
ALTER USER foo PASSWORD EXPIRE DEFAULT;