message: build_conainer: non-root base image fix.
  Part of a fix for non-root invocation of do_ci.sh for regression
  introduced in
diff: @@ -32,3 +32,5 @@ cd /bazel-prebuilt
  for BAZEL_MODE in opt dbg fastbuild; do
  bazel ${BAZEL_OPTIONS} build -c "${BAZEL_MODE}" //bazel/external:all_external
  done
  +# Allow access by non-root for building.
  +chmod -R a+rX /bazel-prebuilt-root /bazel-prebuilt-output
  