Bugfix: POST for remote connect device by serial with body

[StefanHufschmidt]

I faced an error while using remote connect device by serial which told me that I needed to provide a body for this POST request. After adding it it works as expected.

Since this might be beneficial for others as well I decided to open a PR. Feel free to do with it whatever you'd like to do.

[yunusmete]

@StefanHufschmidt Thanks for your contribution. I haven't noticed any change in /remoteConnect. Is that body optional? https://github.com/DeviceFarmer/stf/blob/master/doc/API.md#post-userdevicesserialremoteconnect

Could you try to do the same request with cURL or with an API client like Postman?