Return a list of all available services

    CLI Example:

    .. code-block:: bash

        salt '*' service.get_all

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

    CLI Example:

    .. code-block:: bash

        salt '*' service.get_all
    '''
    if not os.path.isdir(_GRAINMAP.get(__grains__.get('os'), '/etc/init.d')):
        return []
    return sorted(os.listdir(_GRAINMAP.get(__grains__.get('os'), '/etc/init.d')))