(Still tolerate calling it on a no longer (self.)running node, as in a node that has been queried for is_node_stopped() and modified state before returning True).
Tests should not attempt to use the non-functioning RPC interface to call stop() unless wait_for_connections() has succeeded.
No longer log and suppress http.client.CannotSendRequest as a consequence of stop()-RPC, as error conditions causing this knock-on issue are now guarded against before the call.