[Py3] Get python scripts in tools closer to Py3

This modernizes python code without breaking Py2 compat.

Ran with command:

futurize --stage1 -w predictable_wrapper.py
futurize --stage1 -w run-num-fuzzer.py
futurize --stage1 -w run-tests.py
futurize --stage1 -w v8_presubmit.py

This only adds the absolute import, which use these semantics. It
doesn't do anything differently in our case, these scripts are already
doing absolute imports. But with these changes, running `futurize
--stage2` will be less messy.

Bug: v8:9871
Change-Id: I28182ab73dac6cfcbd544c2046026f14e5157eb3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2252555
Reviewed-by: Tamer Tas <tmrts@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68588}

tools/predictable_wrapper.py

@@ -16,6 +16,7 @@ compared. Differences are reported as errors.
 
 
 # for py2/py3 compatibility
+from __future__ import absolute_import
 from __future__ import print_function
 
 import sys

tools/run-num-fuzzer.py

@@ -5,6 +5,7 @@
 # found in the LICENSE file.
 
 
+from __future__ import absolute_import
 import sys
 
 from testrunner import num_fuzzer

tools/run-tests.py

@@ -5,6 +5,7 @@
 # found in the LICENSE file.
 
 
+from __future__ import absolute_import
 import sys
 
 from testrunner import standard_runner

tools/v8_presubmit.py

@@ -29,6 +29,7 @@
 
 
 # for py2/py3 compatibility
+from __future__ import absolute_import
 from __future__ import print_function
 
 try: