## What changes were proposed in this pull request?

Current version has error in vignettes:
```
model <- spark.bisectingKmeans(df, Sepal_Length ~ Sepal_Width, k = 4)
summary(kmeansModel)
```

`kmeansModel` does not exist...

felixcheung wangmiao1981

Author: actuaryzhang <actuaryzhang10@gmail.com>

Closes #16799 from actuaryzhang/sparkRVignettes.