AD: Download master domain info when enumerating
    
    https://fedorahosted.org/sssd/ticket/2068
    
    With the current design, downloading master domain data was tied to
    subdomains refresh, triggered by responders. But because enumeration is
    a background task that can't be triggered on its own, we can't rely on
    responders to download the master domain data and we need to check the
    master domain on each enumeration request.