Get grains for minion.

    .. code-block: bash

        salt '*' nxos.cmd grains

def grains(**kwargs):
    '''
    Get grains for minion.

    .. code-block: bash

        salt '*' nxos.cmd grains
    '''
    if not DEVICE_DETAILS['grains_cache']:
        ret = salt.utils.nxos.system_info(show_ver(**kwargs))
        log.debug(ret)
        DEVICE_DETAILS['grains_cache'].update(ret['nxos'])
    return DEVICE_DETAILS['grains_cache']