Fix some bugs in the luci-config filesystem impl.
Fix some bugs in the luci-config filesystem impl.

R=estaab@chromium.org, nodir@chromium.org
BUG=550684

Review-Url: https://codereview.chromium.org/2003263002

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go