Fix test-http-exceptions

Agent: Each time an http req is sent to a socket, _cycle to try to dispatch
another. Problem became apparent in 4612b0 when we wait for connecting
sockets.

lib/http.js

@@ -1116,6 +1116,7 @@ Agent.prototype._getConnection = function(host, port, cb) {
 // start the process of establishing one.
 Agent.prototype._cycle = function() {
   debug("Agent _cycle sockets=" + this.sockets.length + " queue=" + this.queue.length);
+  var self = this;
 
   var first = this.queue[0];
   if (!first) return;
@@ -1133,6 +1134,7 @@ Agent.prototype._cycle = function() {
       // We found an available connection!
       this.queue.shift(); // remove first from queue.
       first.assignSocket(socket);
+      self._cycle(); // try to dispatch another
       return;
     }