build_docker:  exec the `docker run` command
build_docker:  exec the `docker run` command

The `docker run` command is the last thing that runs; `exec` it for
elegance, and so it doesn't complain when the script changes from
under it.

strahlex/machinekit,strahlex/machinekit,strahlex/machinekit,strahlex/machinekit,strahlex/machinekit,strahlex/machinekit,strahlex/machinekit