fix sysroot-creator.sh's UploadSysroot's gsutil reference

depot_tools seems to have gsutil.py but no gsutil.

BUG=978360

Change-Id: Ib17e3b86e4cf0592a34dcb89224e6ab4d6ecdf2d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1678322Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Mostyn Bramley-Moore <mostynb@vewd.com>
Cr-Commit-Position: refs/heads/master@{#672702}

build/linux/sysroot_scripts/sysroot-creator.sh

@@ -616,7 +616,7 @@ BuildSysrootAll() {
 UploadSysroot() {
   local sha=$(sha1sum "${TARBALL}" | awk '{print $1;}')
   set -x
-  gsutil cp -a public-read "${TARBALL}" \
+  gsutil.py cp -a public-read "${TARBALL}" \
       "gs://chrome-linux-sysroot/toolchain/$sha/"
   set +x
 }