some improvements

[cfz]

the first commit add statistics output to influxdb, so we can monitor the stress real time metrics like error rate and tps. the second commit add a argument validation. we found that if the series number is smaller than the batch size, the current point generation algorithm will generate multiple points with identical timestamp

[desa]

@cfz good work. Would you be able to sign the CLA

• [ ] Sign CLA

[cfz]

done :)