Work around 'ascii' set as the default file path encoding.
Work around 'ascii' set as the default file path encoding.

This is a big assumption that paths are using UTF-8 but this is not the case
only on *BSD and Linux based distributions using exoteric default encoding like
GB18030.

R=vadimsh@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1403843004

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