Fix gsutil PATH priority in base-cipd image

Move the ${CIPD_ROOT}/cipd_bin_packages/gsutil directory before
${CIPD_ROOT}/cipd_bin_packages because gsutil (the directory)
contains gsutil (the executable). Otherwise a process may try
to execute the directory (and fail) instead of the executable.

This didn't come up in testing because /bin/sh is smart enough
to skip over the directory, even though it matches first in the
PATH order. It looks like a Go executable is more literal and
tries to run the first match.

Bug: b/295525434
Change-Id: I7bf981213fa9ccc7bad0d68a3d275e2d303687ea
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/758490
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Auto-Submit: Chris Mumford <cmumford@google.com>

kube/base-cipd/Dockerfile

diff --git a/kube/base-cipd/Dockerfile b/kube/base-cipd/Dockerfile
index 515c469..56210d7 100644
--- a/kube/base-cipd/Dockerfile
+++ b/kube/base-cipd/Dockerfile
@@ -50,4 +50,4 @@
 ARG CIPD_ROOT
 ENV CIPD_ROOT=$CIPD_ROOT
 COPY --from=install_pkgs ${CIPD_ROOT} ${CIPD_ROOT}
-ENV PATH="${CIPD_ROOT}:${CIPD_ROOT}/cipd_bin_packages:${CIPD_ROOT}/cipd_bin_packages/bin:${CIPD_ROOT}/cipd_bin_packages/cpython:${CIPD_ROOT}/cipd_bin_packages/cpython/bin:${CIPD_ROOT}/cipd_bin_packages/cpython3:${CIPD_ROOT}/cipd_bin_packages/cpython3/bin:${CIPD_ROOT}/cipd_bin_packages/gsutil:${PATH}"
+ENV PATH="${CIPD_ROOT}:${CIPD_ROOT}/cipd_bin_packages/gsutil:${CIPD_ROOT}/cipd_bin_packages:${CIPD_ROOT}/cipd_bin_packages/bin:${CIPD_ROOT}/cipd_bin_packages/cpython:${CIPD_ROOT}/cipd_bin_packages/cpython/bin:${CIPD_ROOT}/cipd_bin_packages/cpython3:${CIPD_ROOT}/cipd_bin_packages/cpython3/bin:${PATH}"