8ba8222 Fix memory hierarchy in subdomains discovery

Authored and Committed by jhrozek 8 years ago
    Fix memory hierarchy in subdomains discovery
    
    https://fedorahosted.org/sssd/ticket/1571
    
    The patch changes the subdomains discovery to use the tevent_req
    style. Previously, the code violated several rules which made the code
    very unreadable and led to memory hierarchy issues and use-after-free
    errors.