[SPARK-18873][SQL][TEST] New test cases for scalar subquery (part 1 of 2) -...

[SPARK-18873][SQL][TEST] New test cases for scalar subquery (part 1 of 2) - scalar subquery in SELECT clause

## What changes were proposed in this pull request?
This PR adds new test cases for scalar subquery in SELECT clause.

## How was this patch tested?
The test result is compared with the result run from another SQL engine (in this case is IBM DB2). If the result are equivalent, we assume the result is correct.

Author: Nattavut Sutyanyong <nsy.can@gmail.com>

Closes #16712 from nsyca/18873.