Wait for arnied in addition to generate to preserve backward compatibility

Wait for arnied in addition to generate to preserve backward compatibility

We simplify this a bit though by waiting for the arnied availability
just once during initialization of the cnf store and not on each
get/set/unset_cnf call (now query, commit, and delete calls).

As this is done for backward compability which is guaranteed for
the binary cnfvar driver only, we leave a TODO where we will have
to consider what is the best future for the varlink driver: either
busy-loop on socket availability to once again wait with a timeout
or drop this assumption entirely for better control and easier use.