Make _addNetwork and _delNetwork private

Change-Id: Ie043a26c795a8c8d71a6142d4df45f6584120338
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Signed-off-by: Ido Barkan <ibarkan@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/35311
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>