The default move behavior resets all non-blocking labels (including
Code-Review) which is not generally what we want.  Preserve them.

Change-Id: I9c49582b4147e27d3ed6a439a610c9c667d7aa7e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2586110
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Josip Sokcevic <sokcevic@google.com>