[client] Fix symlink bug
[client] Fix symlink bug

That happens only on task output with a symlink.

Bug: 825418
Change-Id: I0412d7c2438b3a14a19712709c1f98ccab5109a5
Reviewed-on: https://chromium-review.googlesource.com/c/1355723
Reviewed-by: Quinten Yearsley <747cf52e0cef2e3e9371802a2d344b6c87126a4b@chromium.org>
Commit-Queue: Marc-Antoine Ruel <d2bf0fc09b08f7b0888b3ddab32b3e89c7122c8b@chromium.org>

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