gitiles: go back to QueryEscape because url.PathEscape is not in Go1.6.
gitiles: go back to QueryEscape because url.PathEscape is not in Go1.6.

R=hinoka@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2986953002

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