Add device request message

[rbultman]

The current flow of the communications between the devices and the chillhub assumes that the chillhub is already running when devices are plugged into the chillhub. The device subsequently announces itself to the chillhub.

Adding this request message will allow the chillhub to request the device info at any time. This is useful in case the chillhub reboots. It will allow the chillhub to discover connected devices without having to unplug them first.