Unintentional white spaces in kryo classes configuration parameters

## What changes were proposed in this pull request?

Pruned off white spaces present in the user provided comma separated list of classes for **spark.kryo.classesToRegister** and **spark.kryo.registrator**.

## How was this patch tested?

Manual tests

Author: Victor Chima <blazy2k9@gmail.com>

Closes #12701 from blazy2k9/master.