http: fix http agent keep alive

Author: theanarkh

lib/_http_agent.js

@@ -342,7 +342,11 @@ Agent.prototype.createSocket = function createSocket(req, options, cb) {
     installListeners(this, s, options);
     cb(null, s);
   });
-
+  // When keepAlive is true, pass the related options to createConnection
+  if (this.keepAlive) {
+    options.keepAlive = this.keepAlive;
+    options.keepAliveInitialDelay = this.keepAliveMsecs;
+  }
   const newSocket = this.createConnection(options, oncreate);
   if (newSocket)
     oncreate(null, newSocket);