MDEV-22630 mysql_upgrade (MariaDB 5.2.X --> MariaDB 10.3.X) does not fix auth_string to change it to authentication_string

cherry-pick from 10.4:

  commit b976b9bf
  Author: Sergei Golubchik <serg@mariadb.com>
  Date:   Tue Apr 21 18:40:15 2020 +0200

    MDEV-21244 mysql_upgrade creating empty global_priv table

    support upgrades from 5.2 privilege tables