roll_util: Look up CLs by hash not Change-Id

Sometimes a cherry-pick will preserve an existing Change-Id so recipes
can't use it to uniquely identify a CL. Instead of looking up the CL by
Change-Id just use the commit hash which should uniquely identify any
CL.

Change-Id: If39fbb51c8ebbe523a466969a1d8db595b22ee8d
Reviewed-on: https://pigweed-review.googlesource.com/c/infra/recipes/+/42420
Reviewed-by: Marc-Antoine Ruel <maruel@google.com>
Commit-Queue: Rob Mohr <mohrr@google.com>
31 files changed