Support nettest.com also

[bogdanr]

Open Nettest provides an open-source platform for measuring speed. With it, we can measure the speed using servers independent of Ookla or ISPs and there are servers on all continents.

There is a nodejs client that could be used to implement Open Nettest as an alternative to Ookla: https://github.com/specure/open-rmbt-node

[alexjustesen]

Attaching to #976