Port SpawnedTestServer to Python 3

Porting tlslite was more straightforward than it seemed, probably
because they already internally used bytearray everywhere, rather
than str.

One complication is getting a copy of Python 3 onto one of the
CrOS builders. It runs out of space if we ship both Python 2
and Python 3, so I've switched it to only Python 3. This requires
disabling one test, but that test only exists to test Python 2
works.
https://groups.google.com/a/chromium.org/g/python/c/KK60bQcwoCw/m/VctNoDYHCAAJ

We probably should remove GetPythonCommand from //net, since we
don't use it anymore. There's some code in //chrome/browser/media.
But that will take a bit more work to disentangle, so leave it
alone for this CL.

Bug: 1248530
Change-Id: I16b6d077648a436f0f2b42194b19d3104d198614
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3156548
Reviewed-by: Ryan Sleevi <rsleevi@chromium.org>
Reviewed-by: Amr Aboelkher <amraboelkher@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Commit-Queue: David Benjamin <davidben@chromium.org>
Cr-Commit-Position: refs/heads/main@{#922697}
NOKEYCHECK=True
GitOrigin-RevId: 5af020cfe8e17f1d24ce85ee6585d79df0664c6f
8 files changed