Avoid cluttering the home directory by saving the CL description in
the project's working directory.

Bug: None
Change-Id: I42c78d03cd239e7c0453867f21fe4be57086722e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1925627
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>