Update the way urllib is imported. As of Python 3, the old `urllib2`
was split into several smaller modules under `urllib`.

This commit unifies the resulting imported names across Python 2 and
Python 3, for forward/backward compatibility.

Bug: v8:9871
Change-Id: I81310ea83536269ae0cdf1406fd69285928c9357
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2848488Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74209}