[MINOR][SPARKR] fix kstest example error and add unit test

## What changes were proposed in this pull request?

While adding vignettes for kstest, I found some errors in the example:
1. There is a typo of kstest;
2. print.summary.KStest doesn't work with the example;

Fix the example errors;
Add a new unit test for print.summary.KStest;

## How was this patch tested?
Manual test;
Add new unit test;

Author: wm624@hotmail.com <wm624@hotmail.com>

Closes #16259 from wangmiao1981/ks.

(cherry picked from commit f2ddabfa)
Signed-off-by: Yanbo Liang <ybliang8@gmail.com>