schema: fix guest disk mapping versioning

The guest disk mapping report feature is being merged to the ovirt-3.5
branch now, as the current version is 4.16.8 the version on the master
branch should be fixed as well.

Change-Id: I62a532ddef597ecafcdaf454f70dfe5ec2434e1a
Signed-off-by: Liron Aravot <laravot@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/34636
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Piotr Kliczewski <piotr.kliczewski@gmail.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>