[SPARK-22672][SQL][TEST][FOLLOWUP] Fix to use spark.conf

[dongjoon-hyun]

What changes were proposed in this pull request?

During #19882, conf is mistakenly used to switch ORC implementation between native and hive. To affect OrcTest correctly, spark.conf should be used.

How was this patch tested?

Pass the tests.

[SparkQA]

Test build #84673 has finished for PR 19931 at commit b4b1122.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[dongjoon-hyun]

Retest this please

[SparkQA]

Test build #84678 has finished for PR 19931 at commit b4b1122.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[HyukjinKwon]

Merged to master.

[dongjoon-hyun]

Oh, thank you so much, @HyukjinKwon .