Shared task definition / existing services

[robmoorman]

    # Check if all services exist
    existing_services = utils.describe_services(
        connection.ecs, cluster=cluster_name,
        services=task_definitions.keys())

Should this not be services.keys(), as we want to match against service names and not names of task definitions.

Currently it's not possible to run multiple services with a shared task definition (e.g. a celery worker with different queues).