Cleanup fctx->finds before sending 'final' query after qname minimization.

At the beginning of qname minimization we get fctx->finds filled with what's
in the cache at this point, in worst case root servers. After doing full
run querying for NSes at different levels we need to clean it and refill
it with proper values from cache.
27 jobs for 16-cleanup-finds-before-sending-final-query in 8 minutes and 51 seconds (queued for 7 seconds)