Helper function to the grains from the proxied devices.

def _grains():
    '''
    Helper function to the grains from the proxied devices.
    '''
    client = _get_client()
    # This is a collection of the configuration of all running devices under NSO
    ret = client.get_datastore(DatastoreType.RUNNING)
    GRAINS_CACHE.update(ret)
    return GRAINS_CACHE