MDEV-11904 Make Audit Plugin working with MySQL 8.0.
MDEV-11904 Make Audit Plugin working with MySQL 8.0.

        MySQL 8.0 basically inherits the 5.7 model, though some
        modeifications required for the plugin.

natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2