Reland "Update gsutil to use gsutil version 4.68"

This is a reland of commit 8edc960e

Original change's description:
> Update gsutil to use gsutil version 4.68
>
> We can't yet upgrade to version 5.x since it's only py3 compatbile and
> some builders still rely on running gsutil with py2.
>
> R=gavinmak@google.com
>
> Bug: 1184108
> Change-Id: I002cc3625a2184ab42383b88a014c0631d1a33ee
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3508516
> Reviewed-by: Gavin Mak <gavinmak@google.com>
> Commit-Queue: Josip Sokcevic <sokcevic@google.com>

Bug: 1184108
Change-Id: I8f4b726c203ed12d415deeec249972fe855b59c8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3514940Reviewed-by: Brian Ryner <bryner@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>

.gitattributes

@@ -10,8 +10,8 @@
 /*.sh  recipes
 
 # vpython specs
-/.vpython*      recipes
-/gsutil.vpython recipes
+/.vpython*       recipes
+/gsutil.vpython3 recipes
 
 # Extensionless tools we want and support scripts.
 /autoninja*                   recipes

gsutil.py

@@ -34,7 +34,7 @@ DEFAULT_BIN_DIR = os.path.join(THIS_DIR, 'external_bin', 'gsutil')
 
 IS_WINDOWS = os.name == 'nt'
 
-VERSION = '4.28'
+VERSION = '4.68'
 
 
 class InvalidGsutilError(Exception):
@@ -166,8 +166,8 @@ def run_gsutil(target, args, clean=False):
   assert sys.platform != 'cygwin'
 
   cmd = [
-      'vpython',
-      '-vpython-spec', os.path.join(THIS_DIR, 'gsutil.vpython'),
+      'vpython3',
+      '-vpython-spec', os.path.join(THIS_DIR, 'gsutil.vpython3'),
       '--',
       gsutil_bin
   ] + args_opt + args

gsutil.vpython → gsutil.vpython3

@@ -11,92 +11,7 @@
 # "gsutil", where a stock system-deployed file in "/etc/" explicitly specifies
 # that the "google_compute_engine" and "boto" Python packages are available.
 
-python_version: "2.7"
-
-wheel <
-  name: "infra/python/wheels/google_compute_engine-py2_py3"
-  version: "version:2.6.2"
->
-wheel <
-  name: "infra/python/wheels/boto-py2_py3"
-  version: "version:2.48.0"
->
-
-# "gsutil" on non-GCE can require PyOpenSSL, which, in turn, requires
-# "cryptography".
-
-wheel: <
-  name: "infra/python/wheels/pyopenssl-py2_py3"
-  version: "version:17.2.0"
->
-
-##
-# BEGIN "cryptography" dependencies.
-##
-
-wheel: <
-  name: "infra/python/wheels/cryptography/${vpython_platform}"
-  version: "version:2.9.2.chromium.1"
->
-
-wheel: <
-  name: "infra/python/wheels/appdirs-py2_py3"
-  version: "version:1.4.3"
->
-
-wheel: <
-  name: "infra/python/wheels/enum34-py2"
-  version: "version:1.1.6"
->
-
-wheel: <
-  name: "infra/python/wheels/cffi/${vpython_platform}"
-  version: "version:1.14.5.chromium.7"
->
-
-wheel: <
-  name: "infra/python/wheels/idna-py2_py3"
-  version: "version:2.5"
->
-
-wheel: <
-  name: "infra/python/wheels/ipaddress-py2"
-  version: "version:1.0.18"
->
-
-wheel: <
-  name: "infra/python/wheels/packaging-py2_py3"
-  version: "version:16.8"
->
-
-wheel: <
-  name: "infra/python/wheels/pyasn1-py2_py3"
-  version: "version:0.2.3"
->
-
-wheel: <
-  name: "infra/python/wheels/pycparser-py2_py3"
-  version: "version:2.17"
->
-
-wheel: <
-  name: "infra/python/wheels/pyparsing-py2_py3"
-  version: "version:2.2.0"
->
-
-wheel: <
-  name: "infra/python/wheels/setuptools-py2_py3"
-  version: "version:34.3.2"
->
-
-wheel: <
-  name: "infra/python/wheels/six-py2_py3"
-  version: "version:1.10.0"
->
-
-##
-# END "cryptography" dependencies.
-##
+python_version: "3.8"
 
 wheel: <
   name: "infra/python/wheels/crcmod/${vpython_platform}"