refactoring; tweak command layout in Dockerfile
refactoring; tweak command layout in Dockerfile

cyber-dojo/runner_stateless,cyber-dojo/runner_stateless,cyber-dojo/runner_stateless,cyber-dojo/runner_stateless,cyber-dojo/runner,cyber-dojo/runner_stateless,cyber-dojo/runner_stateless,cyber-dojo/runner,cyber-dojo/runner_stateless