[SPARK-23192] [SQL] Keep the Hint after Using Cached Data

[gatorsmile]

What changes were proposed in this pull request?

The hint of the plan segment is lost, when the plan segment is replaced by the cached data.

      val df1 = spark.createDataFrame(Seq((1, "4"), (2, "2"))).toDF("key", "value")
      val df2 = spark.createDataFrame(Seq((1, "1"), (2, "2"))).toDF("key", "value")
      df2.cache()
      val df3 = df1.join(broadcast(df2), Seq("key"), "inner")

This PR is to fix it.

How was this patch tested?

Added a test

[gatorsmile]

cc @cloud-fan @zsxwing @sameeragarwal

[sameeragarwal]

LGTM

[dongjoon-hyun]

+1, LGTM.

[SparkQA]

Test build #86536 has finished for PR 20365 at commit 1186ef5.

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

[jiangxb1987]

retest this please

[SparkQA]

Test build #86544 has finished for PR 20365 at commit 1186ef5.

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

[gatorsmile]

Since the last change is just to change the test case name, I merge this PR.

[gatorsmile]

Thanks! Merged to master/2.3

[SparkQA]

Test build #86546 has finished for PR 20365 at commit 7209792.

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