PRESUBMIT.cfg: run presubmit.py checks more cleanly.

Run the presubmit checks the same way that `git cl presubmit` does.

BUG=chromium:1149626
TEST=manual

Change-Id: Ifc510f556d38e499fb8c62fe653985738995dd9b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/2552264
Commit-Queue: LaMont Jones <lamontjones@chromium.org>
Commit-Queue: Sean McAllister <smcallis@google.com>
Tested-by: LaMont Jones <lamontjones@chromium.org>
Auto-Submit: LaMont Jones <lamontjones@chromium.org>
Reviewed-by: Sean McAllister <smcallis@google.com>
diff --git a/PRESUBMIT.cfg b/PRESUBMIT.cfg
index 70fc395..5614d28 100644
--- a/PRESUBMIT.cfg
+++ b/PRESUBMIT.cfg
@@ -8,7 +8,7 @@
 long_line_check: true
 
 [Hook Scripts]
-git_cl_presubmit = presubmit_support.py $(if [[ "${PRESUBMIT_COMMIT}" = pre-submit ]]; then echo --commit; fi)
+git_cl_presubmit = vpython3 $(which presubmit_support.py) $(if [[ "${PRESUBMIT_COMMIT}" = pre-submit ]]; then echo --commit; fi)
 # If running in the chroot, EPYTHON ensures the wrappers don't get the wrong
 # version.
 pylint = EPYTHON=python2 ./utils/run_pylint.py