[SSSD] [PATCH] Only do one cycle when resolving a server

[Jakub Hrozek]

https://fedorahosted.org/sssd/ticket/1214

I was actually going back and forth on the implementation -- my first
approach was to separate requests for "beginning to resolve a service" and
"give me another server for this service".

I think that is more natural way to perform the resolution, but it turned out
that this approach would require bigger changes to the back ends and I'm not
sure if I can justify that just for the sake of nicer code at this point of
1.8 development. I still have a WIP patch that builds, should we decide that
it's actually better to separate requests for first and any next server..