AD: initialize failover with custom realm, domain and failover service
    
    This is needed so we can initialize failover using IPA realm and
    on-the-fly discovered DNS domain. The subdomains discovered on-thefly
    will use the subdomain name for realm, domain and failover service to
    avoid conflicts.
    
    Subtaks of:
    https://fedorahosted.org/sssd/ticket/1962