To use the dockerized build, replace ./build.sh with ./docker-build.sh in your commandline.
The script constructs a container and starts it. In the container several environment parameters
are fixed:
  * the base OS: Ubuntu 14.04 LTS
  * the hostname: "ffpb-build"
  * the source directory: /code

In theory, this should be enough to get the same build output no matter where the firmware gets
compiled and/or by whom.