Make file_path.py python 2.6 compatible.
Make file_path.py python 2.6 compatible.

This is because the chromium fleet still has a few cygwin setup still running
python 2.6.

R=vadimsh@chromium.org
BUG=chromium:379232

Review URL: https://codereview.appspot.com/191930043

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py