[LIVY-531][BUILD] Update spark-2.3 default version to 2.3.2
[LIVY-531][BUILD] Update spark-2.3 default version to 2.3.2

## What changes were proposed in this pull request?

Due to spark 2.3.2 is highly recommended version to upgrade for all 2.3.x users which contains many stability bug fixes.

## How was this patch tested?

Existing UTs.

Author: Lantao Jin <jinlantao@gmail.com>

Closes #124 from LantaoJin/LIVY-531.

meisam/incubator-livy,ajbozarth/incubator-livy,meisam/incubator-livy,ajbozarth/incubator-livy,ajbozarth/incubator-livy,ajbozarth/incubator-livy,meisam/incubator-livy,ajbozarth/incubator-livy,meisam/incubator-livy,meisam/incubator-livy,meisam/incubator-livy,ajbozarth/incubator-livy