DNS: Fix upgrade - master to forward zone transformation
    
    This happens when upgrading from IPA <= 4.0 to versions 4.3+.
    
    DNS caching might cause false positive in code which replaces master zone
    with forward zone. This will effectivelly delete the master zone
    without adding a replacement forward zone.
    
    Solution is to use skip_overlap_check option for dnsforwardzone_add command
    so zone existence check is skipped and the upgrade can proceed.
    
    https://fedorahosted.org/freeipa/ticket/5851
    
    Reviewed-By: Martin Basti <mbasti@redhat.com>