[SPARK-22120][SQL] TestHiveSparkSession.reset() should clean out Hive warehouse directory

## What changes were proposed in this pull request?
During TestHiveSparkSession.reset(), which is called after each TestHiveSingleton suite, we now delete and recreate the Hive warehouse directory.

## How was this patch tested?
Ran full suite of tests locally, verified that they pass.

Author: Greg Owen <greg@databricks.com>

Closes #19341 from GregOwen/SPARK-22120.