[SPARK-21982] Set locale to US

## What changes were proposed in this pull request?

In UtilsSuite Locale was set by default to US, but at the moment of using format function it wasn't, taking by default JVM locale which could be different than US making this test fail.

## How was this patch tested?
Unit test (UtilsSuite)

Author: German Schiavon <germanschiavon@gmail.com>

Closes #19205 from Gschiavon/fix/test-locale.