[Py3] Get tools/testrunner closer to Py3

This modernizes python code without breaking Py2 compat.

Ran with command:

futurize --stage1 -w tools/testrunner

Bug: v8:9871
Change-Id: Ie23333cbd923197be0bffcad5041056e00990042
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2252554
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Tamer Tas <tmrts@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68496}

tools/testrunner/num_fuzzer.py

@@ -5,13 +5,14 @@
 # found in the LICENSE file.
 
 # for py2/py3 compatibility
+from __future__ import absolute_import
 from __future__ import print_function
 
 import random
 import sys
 
 # Adds testrunner to the path hence it has to be imported at the beggining.
-import base_runner
+from . import base_runner
 
 from testrunner.local import utils
 

tools/testrunner/standard_runner.py

@@ -5,6 +5,7 @@
 # found in the LICENSE file.
 
 # for py2/py3 compatibility
+from __future__ import absolute_import
 from __future__ import print_function
 from functools import reduce
 
@@ -15,7 +16,7 @@ import sys
 import tempfile
 
 # Adds testrunner to the path hence it has to be imported at the beggining.
-import base_runner
+from . import base_runner
 
 from testrunner.local import utils
 from testrunner.local.variants import ALL_VARIANTS