Return a list of all available services

    CLI Example:

    .. code-block:: bash

        salt '*' s6.get_all

def get_all():
    '''
    Return a list of all available services

    CLI Example:

    .. code-block:: bash

        salt '*' s6.get_all
    '''
    if not SERVICE_DIR:
        raise CommandExecutionError("Could not find service directory.")
    service_list = [dirname for dirname
                            in os.listdir(SERVICE_DIR)
                            if not dirname.startswith('.')]
    return sorted(service_list)