When the /system/info endpoint was expanded to include information about the gateway a number of build-args were added to the main Dockerfile.  These changes were not mirrored in Dockerfile.armhf, which resulted in nil attributes and an ugly error when running `faas version` against an armhf gateway.

This change carries the changes made to Dockerfile through to Dockerfile.armhf.  As well as the build-args which fix the identified issue the license check has also been added at the latest release 0.2.3, as a armhf build has been made available.  Further changes are to introduce the app user and moving the binary location from /root/ to /home/app/

Signed-off-by: Richard Gee <richard@technologee.co.uk>