added error handling when HTTP proxy doesn't connect

lib/modules/http.js

@@ -64,6 +64,18 @@ module.exports.create = function (deps, conf) {
       proxyReq.setHeader('X-Forwarded-For', opts.remoteAddress || conn.remoteAddress);
     });
 
+    proxy.on('error', function (err, req, res) {
+      console.log(err);
+      res.writeHead(502);
+      if (err.code === 'ECONNREFUSED') {
+        res.end('The connection was refused. Most likely the service being connected to '
+          + 'has stopped running or the configuration is wrong.');
+      }
+      else {
+        res.end('Bad Gateway: ' + err.code);
+      }
+    });
+
     return function (req, res, next) {
       var hostname = req.headers.host.split(':')[0];
       var relevant = mod.domains.some(function (pattern) {