[ML][MINOR] Separate estimator and model params for read/write test.

## What changes were proposed in this pull request?
Since we allow ```Estimator``` and ```Model``` not always share same params (see ```ALSParams``` and ```ALSModelParams```), we should pass in test params for estimator and model separately in function ```testEstimatorAndModelReadWrite```.

## How was this patch tested?
Existing tests.

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #17151 from yanboliang/test-rw.