[SPARK-17409][SQL][FOLLOW-UP] Do Not Optimize Query in CTAS More Than Once

### What changes were proposed in this pull request?
This follow-up PR is for addressing the [comment](https://github.com/apache/spark/pull/15048).

We added two test cases based on the suggestion from yhuai . One is a new test case using the `saveAsTable` API to create a data source table. Another is for CTAS on Hive serde table.

Note: No need to backport this PR to 2.0. Will submit a new PR to backport the whole fix with new test cases to Spark 2.0

### How was this patch tested?
N/A

Author: gatorsmile <gatorsmile@gmail.com>

Closes #15459 from gatorsmile/ctasOptimizedTestCases.