The REST endpoint used by GerritClient.ListOwners needs to be updated as
of https://gerrit-review.googlesource.com/c/plugins/code-owners/+/293806

Change-Id: I5c142f16443b157c9d8edfa5bcf418cbedd2b193
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2658609Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Gavin Mak <gavinmak@google.com>