This will cycle through known gerrit mirrors for chromium-review host
if Gerrit HTTP RPC results in 404 after successful initial
git push refs/for/refs/...

Tested locally by intentionally using wrong change number (2000000):

    $ PATH=`pwd`:$PATH git cl upload --bypass-hooks
        ...
        remote: Processing changes: refs: 1, new: 1, done
        remote: SUCCESS
        remote: New Changes:
        remote:   https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1227440

                * [new branch]        ea9aea5faa85b4b289b7add4bc6f4d5dd6a01caf -> refs/for/refs/heads/master%wip,m=Initial_upload,hashtag=git-cl

        WARNING:root:404 NotFound error occurred while querying POST https://chromium-review.googlesource.com/a/changes/chromium%2Ftools%2Fdepot_tools~2000000/revisions/current/review: Not Found
        WARNING:root:404 NotFound error occurred while querying POST https://ap1-mirror-chromium-review.googlesource.com/a/changes/chromium%2Ftools%2Fdepot_tools~2000000/revisions/current/review: Not Found
        WARNING:root:404 NotFound error occurred while querying POST https://us1-mirror-chromium-review.googlesource.com/a/changes/chromium%2Ftools%2Fdepot_tools~2000000/revisions/current/review: Not Found

        ^C

Bug: 881860
Change-Id: Iac7dbe4e35052007650a7a2646a394caed6bd400
Reviewed-on: https://chromium-review.googlesource.com/1227441
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>