Add option to build development version of the gateway (#1605)
Add option to build development version of the gateway (#1605)

* Add option to build development version of the gateway
* Changed test to allow DEV_BUILD to be empty string

mozilla-iot/gateway,mozilla-iot/gateway,mozilla-iot/gateway,moziot/gateway,mozilla-iot/gateway,mozilla-iot/gateway,moziot/gateway,moziot/gateway