refactoring; move validation calls out of runner.initialize() as step towards removing them from runner.run()
refactoring; move validation calls out of runner.initialize() as step towards removing them from runner.run()

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