Ping AOS before making requests

[AndreasHassing]

The AOSClient currently retries its actions on timeout - which is fine for the most part. But instead of showing the user a confusing error message like:

System.Threading.Tasks.TaskCanceledException: The operation was canceled.
---> System.IO.IOException: Unable to read data from the transport connection: The I/O operation has been aborted because of either a thread exit or an application request..
---> System.Net.Sockets.SocketException (995): The I/O operation has been aborted because of either a thread exit or an application request.

we should ping the AOS first to ensure it is warm before trying to perform ALM requests.

I'm not sure, but I expect an authenticated app can ping the AOS at the POST /ping endpoint and expect a 200 - OK to mean that the AOS is up and running.