mass-abandon allows users to mass abandon CLs based on search query.
Owner is always specified (either "me" or user defined via -p).

R=gavinmak@google.com, thakis@chromium.org

Change-Id: I789a3a1f3af22867ebbbc50c35b60486206ff403
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2811005Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>