Discovery returns after 16 responses even if there are no coord responses

Discovery sets Responses.num_expected_rsps to 16 if no member list is defined. This makes discovery return after 16 responses even if no response from a coordinator has been received.
This is a problem if we have a cluster of size > 16 and the coordinator doesn't respond imediately, e.g. because it is busy processing other requests.

Solution

• Set num_expected_rsps to 0 (= wait until at least 1 coord rsp has been received