corehttp: ensure node closing/teardown waits for server termination

When closing a node, the node itself only takes care of tearing down
its own children. As corehttp sets up a server based on a node, it
needs to also ensure that the server is accounted for when determining
if the node has been fully closed.

core/corehttp/corehttp.go

@@ -64,6 +64,9 @@ func listenAndServe(node *core.IpfsNode, addr ma.Multiaddr, handler http.Handler
 	var serverError error
 	serverExited := make(chan struct{})
 
+	node.Children().Add(1)
+	defer node.Children().Done()
+
 	go func() {
 		serverError = server.ListenAndServe(host, handler)
 		close(serverExited)