bindinstance: use data in named.conf to determine configuration status
    
    Instead of checking sysrestore status which leads to incorrect
    evaluation of DNS configuration status during 4.2 -> 4.4 upgrade, look
    into named.conf to see whther it was already modified by IPA installer.
    
    https://fedorahosted.org/freeipa/ticket/6503
    
    Reviewed-By: Martin Basti <mbasti@redhat.com>