add __nowating flag to cluster config, see issue #803

examples/cluster2.lua

@@ -22,6 +22,7 @@ skynet.start(function()
 		}
 		print(pcall(cluster.call, "db", "@sdb", "GET", "a"))	-- db is down
 	end)
+	cluster.reload { __nowaiting = false }
 	local pingserver = cluster.snax("db3", "pingserver")
 	print(pingserver.req.ping "hello")
 end)

examples/clustername.lua

@@ -1,2 +1,4 @@
+__nowaiting = true	-- If you turn this flag off, cluster.call would block when node name is absent
+
 db = "127.0.0.1:2528"
 db2 = "127.0.0.1:2529"