[SPARK-15417][SQL][PYTHON] PySpark shell always uses in-memory catalog

## What changes were proposed in this pull request?

There is no way to use the Hive catalog in `pyspark-shell`. This is because we used to create a `SparkContext` before calling `SparkSession.enableHiveSupport().getOrCreate()`, which just gets the existing `SparkContext` instead of creating a new one. As a result, `spark.sql.catalogImplementation` was never propagated.

## How was this patch tested?

Manual.

Author: Andrew Or <andrew@databricks.com>

Closes #13203 from andrewor14/fix-pyspark-shell.