Fix internal errors in host-add and other commands caused by DNS resolution
    
    Previously resolver was returning CheckedIPAddress objects. This
    internal server error in cases where DNS actually returned reserved IP
    addresses.
    
    Now the resolver is returning UnsafeIPAddress objects which do syntactic
    checks but do not filter IP addresses.
    
    From now on we can decide if some IP address should be accepted as-is or
    if it needs to be contrained to some subset of IP addresses using
    CheckedIPAddress class.
    
    This regression was caused by changes for
    https://fedorahosted.org/freeipa/ticket/5710
    
    Reviewed-By: Martin Basti <mbasti@redhat.com>