Simplify when to detach the client

Simplify when to detach the client

With stale-answer-client-timeout, we may send a response to the client,
but we may want to hold on to the network manager handle, because
recursion is going on in the background, or we need to refresh a
stale RRset.

Simplify the setting of 'nodetach':
* During a staleonly lookup we should not detach the nmhandle, so just
  set it prior to 'query_lookup()'.
* During a staleonly "stalefirst" lookup set the 'nodetach' to true
  if we are going to refresh the RRset.

Now there is no longer the need to clear the 'nodetach' if we go
through the "dbfind_stale", "stale_refresh_window", or "stale_only"
paths.