[feature] Use argo_nodeos_config --exec
Use the new argo_nodeos_config --exec feature in development. Allow us to delegate fork+attach+exec to argo_nodeos_config, and simplifying the create command as a result. We use tornado.process to wrap this command, as we want to able to stream stdout/stderr in the future. This patch also misuse, the 'pid' field of the container namedtuple to save the tornado.process.Subprocess object itself, so some functions need to be adapted.