roll_util: Support multi-roll commit messages

Support roll messages for rolls of multiple submodules or repo projects.
Not yet used.

Change-Id: I8a5c4c5b3e141835e720cfd16e77f9122717b3e6
Reviewed-on: https://pigweed-review.googlesource.com/c/infra/recipes/+/22404
Commit-Queue: Rob Mohr <mohrr@google.com>
Reviewed-by: Oliver Newman <olivernewman@google.com>
24 files changed
tree: 30b722321ac9815850ae0b59ec4b53e34610ae9c
  1. infra/
  2. recipe_modules/
  3. recipes/
  4. .gitignore
  5. .style.yapf
  6. recipes.py