[Python] Use consistent import ordering for Python code

Ordering used:
1.) standard library imports
2.) third party imports
3.) local package imports

Each group is individually alphabetized.

benchmark/scripts/perf_test_driver/perf_test_driver.py

@@ -12,10 +12,10 @@
 #
 # ===----------------------------------------------------------------------===//
 
-import os
-import subprocess
 import multiprocessing
+import os
 import re
+import subprocess
 
 class Result(object):
     def __init__(self, name, status, output, xfail_list):