path module: fix tmp / cache dir creation
path module: fix tmp / cache dir creation

CL d87e1df614c1b51a4bd09d9fd947fecc0c096f8b had type mismatch. Fix that.

TBR=iannucci@chromium.org
BUG=683410

Review-Url: https://codereview.chromium.org/2653073003

luci/recipes-py,luci/recipes-py