[SPARK-20779][EXAMPLES] The ASF header placed in an incorrect location in some files.

## What changes were proposed in this pull request?

The license is not at the top in some files. and it will be best if we update these places of the ASF header to be consistent with other files.

## How was this patch tested?

manual tests

Author: zuotingbing <zuo.tingbing9@zte.com.cn>

Closes #18012 from zuotingbing/spark-license.

examples/src/main/python/parquet_inputformat.py

-from __future__ import print_function
 #
 # Licensed to the Apache Software Foundation (ASF) under one or more
 # contributor license agreements.  See the NOTICE file distributed with
@@ -16,6 +15,8 @@ from __future__ import print_function
 # limitations under the License.
 #
 
+from __future__ import print_function
+
 import sys
 
 from pyspark.sql import SparkSession

examples/src/main/python/pi.py

-from __future__ import print_function
 #
 # Licensed to the Apache Software Foundation (ASF) under one or more
 # contributor license agreements.  See the NOTICE file distributed with
@@ -16,6 +15,8 @@ from __future__ import print_function
 # limitations under the License.
 #
 
+from __future__ import print_function
+
 import sys
 from random import random
 from operator import add