[SPARK-19583][SQL] CTAS for data source table with a created location should succeed

## What changes were proposed in this pull request?

```
  spark.sql(
          s"""
             |CREATE TABLE t
             |USING parquet
             |PARTITIONED BY(a, b)
             |LOCATION '$dir'
             |AS SELECT 3 as a, 4 as b, 1 as c, 2 as d
           """.stripMargin)
```

Failed with the error message:
```
path file:/private/var/folders/6r/15tqm8hn3ldb3rmbfqm1gf4c0000gn/T/spark-195cd513-428a-4df9-b196-87db0c73e772 already exists.;
org.apache.spark.sql.AnalysisException: path file:/private/var/folders/6r/15tqm8hn3ldb3rmbfqm1gf4c0000gn/T/spark-195cd513-428a-4df9-b196-87db0c73e772 already exists.;
	at org.apache.spark.sql.execution.datasources.InsertIntoHadoopFsRelationCommand.run(InsertIntoHadoopFsRelationCommand.scala:102)
```
while hive table is ok ,so we should fix it for datasource table.

The reason is that the SaveMode check is put in  `InsertIntoHadoopFsRelationCommand` , and the SaveMode check actually use `path`, this is fine when we use `DataFrameWriter.save()`, because this situation of SaveMode act on `path`.

While when we use  `CreateDataSourceAsSelectCommand`, the situation of SaveMode act on table, and
we have already do SaveMode check in `CreateDataSourceAsSelectCommand` for table , so we should not do SaveMode check in the following logic in `InsertIntoHadoopFsRelationCommand` for path, this is redundant and wrong logic for `CreateDataSourceAsSelectCommand`

After this PR, the following DDL will succeed, when the location has been created we will append it or overwrite it.
```
CREATE TABLE ... (PARTITIONED BY ...) LOCATION path AS SELECT ...
```

## How was this patch tested?
unit test added

Author: windpiger <songjun@outlook.com>

Closes #16938 from windpiger/CTASDataSourceWitLocation.

1 files changed, 2 insertions, 2 deletions

diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/command/createDataSourceTables.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/command/createDataSourceTables.scala
index 5abd579476..d835b52116 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/command/createDataSourceTables.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/command/createDataSourceTables.scala
@@ -141,7 +141,7 @@ case class CreateDataSourceTableAsSelectCommand(
       }
 
       saveDataIntoTable(
-        sparkSession, table, table.storage.locationUri, query, mode, tableExists = true)
+        sparkSession, table, table.storage.locationUri, query, SaveMode.Append, tableExists = true)
     } else {
       assert(table.schema.isEmpty)
 
@@ -151,7 +151,7 @@ case class CreateDataSourceTableAsSelectCommand(
         table.storage.locationUri
       }
       val result = saveDataIntoTable(
-        sparkSession, table, tableLocation, query, mode, tableExists = false)
+        sparkSession, table, tableLocation, query, SaveMode.Overwrite, tableExists = false)
       val newTable = table.copy(
         storage = table.storage.copy(locationUri = tableLocation),
         // We will use the schema of resolved.relation as the schema of the table (instead of