Add check for device not found

https://github.com/appium/appium/issues/2995
if the purpose of this line is to get us back into the retry loop after reconnecting devices, then it needs to be inside the callback above. putting it here will potentially lead to an async bug. it should look like (i think):

```js
setTimeout(function () {
  this.adb.getDevicesWithRetry(function (err, devices) {
    if (err) return _cb(new Error("Recconect failed, devices are: " + devices));
    _cb(new Error(stderr)); // we've reconnected, so get back into the retry loop
  });
}.bind(this), 1000);
```