This modernizes python code without breaking Py2 compat.

Ran with command:

futurize --stage1 -w tools/testrunner

and manual fixup in statusfile_unittest.py to change to update import
path and change to absolute imports (similar to pool_unittest.py)

Bug: v8:9871
Change-Id: I8851e2188ef9285f2bd57cc07e959e22e1b05f6b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2252548Reviewed-by: Tamer Tas <tmrts@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68490}