cluster: support setting data on shared server

If `obj` given to `cluster._getServer` has `_setServerData` or
`_getServerData` methods, the data will be synchronized across workers
and stored in master.

lib/cluster.js

@@ -384,8 +384,15 @@ function masterInit() {
                                               message.backlog,
                                               message.fd);
     }
+    if (!handle.data) handle.data = message.data;
+
+    // Set custom server data
     handle.add(worker, function(errno, reply, handle) {
-      reply = util._extend({ ack: message.seq, key: key }, reply);
+      reply = util._extend({
+        ack: message.seq,
+        key: key,
+        data: handles[key].data
+      }, reply);
       if (errno) {
         reply.errno = errno;
         delete handles[key];  // Gives other workers a chance to retry.
@@ -447,9 +454,14 @@ function workerInit() {
       address: address,
       port: port,
       act: 'queryServer',
-      fd: fd
+      fd: fd,
+      data: null
     };
+    // Set custom data on handle (i.e. tls tickets key)
+    if (obj._getServerData) message.data = obj._getServerData();
     send(message, function(reply, handle) {
+      if (obj._setServerData) obj._setServerData(reply.data);
+
       if (handle)
         shared(reply, handle, cb);  // Shared listen socket.
       else