enable zmq curve security #552

we should be able to enable basic CURVE security by setting CURVE_PRIVATEKEY an CURVE_SERVER on the server sockets, and CURVE_SERVERKEY and private/public on the engine/client side, and distributing the server key in our existing connection files.

ZAP gives us more detailed auth controls, but I think simple key distribution should work well enough for us, and ZAP would be hard to deploy for the multi-process controller, since each Context (aka each Process) needs a ZAP thread.