[SPARK-21914][FOLLOWUP][test-hadoop3.2][test-java11] Clone SparkSession per each function example

[MaxGekk]

What changes were proposed in this pull request?

In the PR, I propose to clone Spark session per-each expression example. Examples can modify SQL settings, and can influence on each other if they run in the same Spark session in parallel.

Why are the changes needed?

This should fix test failures like this checking of the Like example:

org.apache.spark.sql.AnalysisException: the pattern '\%SystemDrive\%\Users%' is invalid, the escape character is not allowed to precede 'U';
      at org.apache.spark.sql.catalyst.util.StringUtils$.fail$1(StringUtils.scala:48)
      at org.apache.spark.sql.catalyst.util.StringUtils$.escapeLikeRegex(StringUtils.scala:57)
      at org.apache.spark.sql.catalyst.expressions.Like.escape(regexpExpressions.scala:108)

Does this PR introduce any user-facing change?

No

How was this patch tested?

By running check outputs of expression examples in org.apache.spark.sql.SQLQuerySuite

[SparkQA]

Test build #111521 has finished for PR 25956 at commit 75fe88d.

• This patch fails due to an unknown error code, -9.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #111522 has finished for PR 25956 at commit 75fe88d.

• This patch fails due to an unknown error code, -9.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #111523 has finished for PR 25956 at commit 75fe88d.

• This patch fails due to an unknown error code, -9.
• This patch merges cleanly.
• This patch adds no public classes.

[MaxGekk]

jenkins, retest this, please

[SparkQA]

Test build #111526 has finished for PR 25956 at commit 75fe88d.

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

[MaxGekk]

jenkins, retest this, please

[SparkQA]

Test build #111528 has finished for PR 25956 at commit 75fe88d.

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

[MaxGekk]

jenkins, retest this, please

[MaxGekk]

@HyukjinKwon @wangyum @dongjoon-hyun Take a look at this PR, please.

[SparkQA]

Test build #111530 has finished for PR 25956 at commit 75fe88d.

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

[SparkQA]

Test build #111533 has finished for PR 25956 at commit 75fe88d.

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

[HyukjinKwon]

Merged to master.