if we are downloading an app, actually listen for the error event (add better logs for #4832)

lib/devices/device.js

@@ -116,7 +116,8 @@ Device.prototype.configureDownloadedApp = function (cb) {
   var ext = path.extname(appUrl.pathname);
   if (ext === ".apk") {
     try {
-      downloadFile(url.format(appUrl), ".apk", function (appPath) {
+      downloadFile(url.format(appUrl), ".apk", function (err, appPath) {
+        if (err) return cb(err);
         this.tempFiles.push(appPath);
         this.args.app = appPath;
         cb();
@@ -174,7 +175,8 @@ Device.prototype.unzipApp = function (zipPath, cb) {
 };
 
 Device.prototype.downloadAndUnzipApp = function (appUrl, cb) {
-  downloadFile(appUrl, ".zip", function (zipPath) {
+  downloadFile(appUrl, ".zip", function (err, zipPath) {
+    if (err) return cb(err);
     this.unzipApp(zipPath, cb);
   }.bind(this));
 };

lib/helpers.js

@@ -18,13 +18,20 @@ var logger = require('./server/logger.js').get('appium')
 exports.downloadFile = function (fileUrl, suffix, cb) {
   // We will be downloading the files to a directory, so make sure it's there
   // This step is not required if you have manually created the directory
+  cb = _.once(cb);
   tempDir.open({prefix: 'appium-app', suffix: suffix}).nodeify(function (err, info) {
     fs.close(info.fd);
     var file = fs.createWriteStream(info.path);
-    request(fileUrl).pipe(file).on('close', function () {
-      logger.debug(fileUrl + ' downloaded to ' + info.path);
-      cb(info.path);
-    });
+    request(fileUrl)
+      .on('error', function (err) {
+        logger.error("Problem downloading file: " + err.message);
+        cb(err);
+      })
+      .pipe(file)
+      .on('close', function () {
+        logger.debug(fileUrl + ' downloaded to ' + info.path);
+        cb(null, info.path);
+      });
   });
 };