Use docker-compose to start bash inside the master container

[kinow]

Hi,

On my Ubuntu LTS, following the README.md instructions (really helpful! Thanks!) I got almost everything working without having to change the commands.

The exception was how to run bash in the master container. The command suggested in the README.md appears to be platform and/or version dependent. On my local environment it the container has a different name, so it fails to run bash.

kinow@ranma:/tmp/docker-compss-runtime$ docker exec -it deephealth_compss-master_1 bash
Error: No such container: deephealth_compss-master_1

This PR uses the docker-compose command, where we can use the service name.

docker-compose exec compss-master bash

[kinow]

I think an alternative could be to set the container_name in docker-compose.yaml.