MySQL-5.7 mysql.user tables have a last_password_changed field.

Because before MariaDB-10.4 remained oblivious to this, the act of creating
users or otherwise changing a users row left the last_password_field with 0.

Running a MariaDB-10.4 instance on this would work correctly, until mysql_upgrade
is run, when this 0 value immediately translates to password expired
state.

MySQL-5.7 relied on the password_expired enum to indicate password
expiry so we aren't going to activate password that were expired in
MySQL-5.7.

Thanks Hans Borresen for the bug report and review of the fix.