git cl owners orders owners by score with alphabetization being the tie
breaker. This leads to some owners being suggested far more often than
others.

Adding a tiny amount of randomization to the scoring leads to an even
distribution of equally qualified reviewers. Less qualified reviewers
will still be sorted into distinct buckets - the randomness is too small
to do anything except break ties.

The tests were updated so that they can tolerate the randomness, but
only for breaking ties.

Bug: 1024083
Change-Id: If7d39d1b3bbd980b80b46ab3f62c65215309bdc8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1913642
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Anthony Polito <apolito@google.com>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>