Add proper ping function implementation

[kaolpr]

This function should communicate with the device (e.g. read device model) and return True if the response was as expected. See ARTIQ manual for details.

[mmalczak]

In this manual:
https://m-labs.hk/artiq/manual/developing_a_ndsp.html
there is the following description:

In order to be correctly started and stopped by a controller manager, your controller must additionally implement a ping() method, which should simply return true, e.g.
def ping(self):
return True

Could you please point me to the manual you mean, with proper description?

[mmalczak]

Nevermind, I will take different NDSP as an example.