Updating config while tests run

[aecay]

Mite has the ability to propagate changes in the ConfigManager to runners after the initial setup. In each call to Controller.request_work, a dictionary diff is computed (via ConfigManager.get_changes_for_runner) and sent over the wire; this is unpacked in the runner.

But as far as I can tell, this feature is never used. The only call to ConfigManager.set in the mite code is in __main__._create_config_manager (which is called at startup). I could not find any calls either in the id-mite-nft data repo.

[aecay]

From @jb098 in #15:

It would obviously need some thought about how we wanted a live config to operate. Either providing a zmq admin channel, a http endpoint or have it refresh from env vars at regular intervals.

[aecay]

We might want to implement a new message type for this, rather than passing a (almost always empty) dict of config changes on every communication from the controller to the runner.