[swarming] standardize state 'cwd'.
[swarming] standardize state 'cwd'.

Otherwise we get a mix of 'c:\' and 'C:\' which is annoying.

Change-Id: I78b2af348ea7c58beba76f26a2138d9bac2ce9aa
Reviewed-on: https://chromium-review.googlesource.com/1051006
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