[gsutil] run through "vpython"

Run "gsutil" through "vpython". This ensures that the package set
accompanying it is completely controlled. This is notably important on
GCE instances, which "gsutil" expects to supply a
"google_compute_engine" package.

BUG=None
TEST=local
  - Ran `gsutil cp` on 64-bit Linux machine, seems to work.
  - Ran `gsutil cp` on GCE instance, seems to work.

Change-Id: Id771bc4da4de22c941b0ace4031cb0f3364feeeb
Reviewed-on: https://chromium-review.googlesource.com/527277
Reviewed-by: Nodir Turakulov <nodir@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Daniel Jacques <dnj@chromium.org>

gsutil.py

@@ -29,6 +29,9 @@ DEFAULT_BIN_DIR = os.path.join(THIS_DIR, 'external_bin', 'gsutil')
 DEFAULT_FALLBACK_GSUTIL = os.path.join(
     THIS_DIR, 'third_party', 'gsutil', 'gsutil')
 
+IS_WINDOWS = os.name == 'nt'
+
+
 class InvalidGsutilError(Exception):
   pass
 
@@ -126,8 +129,17 @@ def run_gsutil(force_version, fallback, target, args, clean=False):
   else:
     gsutil_bin = fallback
   disable_update = ['-o', 'GSUtil:software_update_check_period=0']
-  cmd = [sys.executable, gsutil_bin] + disable_update + args
-  return subprocess.call(cmd)
+
+  # Run "gsutil" through "vpython". We need to do this because on GCE instances,
+  # expectations are made about Python having access to "google-compute-engine"
+  # and "boto" packages that are not met with non-system Python (e.g., bundles).
+  cmd = [
+      'vpython',
+      '-vpython-spec', os.path.join(THIS_DIR, 'gsutil.vpython'),
+      '--',
+      gsutil_bin
+  ] + disable_update + args
+  return subprocess.call(cmd, shell=IS_WINDOWS)
 
 
 def parse_args():

gsutil.vpython

@@ -0,0 +1,21 @@
+# vpython VirtualEnv protobuf for "gsutil".
+#
+# See:
+# https://chromium.googlesource.com/infra/luci/luci-go/+/master/vpython/api/vpython/spec.proto
+#
+# This is a "vpython" VirtualEnv specification applied to invocations of "gsutil"
+# by the bootstrap wrapper, "gsutil.py". It ensures that any Python distribution
+# has the expected Python packages installed.
+#
+# This is specifically relevant on Google Compute Engine invocations of
+# "gsutil", where a stock system-deployed file in "/etc/" explicitly specifies
+# that the "google_compute_engine" and "boto" Python packages are available.
+
+wheel <
+  name: "infra/python/wheels/google_compute_engine-py2_py3"
+  version: "version:2.3.7"
+>
+wheel <
+  name: "infra/python/wheels/boto-py2_py3"
+  version: "version:2.47.0"
+>