test_planner: implement new only-test functionality

This lets us say something like "if a CQ run only affects
chromite, then only run tests on kevin".

I had to refactor things a bit to express this sort-of cleanly.

BUG=chromium:976530
TEST=unit tests, local run

Change-Id: I59aefb9ce082990d53d7f8b5adff1643e7c99bfd
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/test_planner/+/1673802
Reviewed-by: Sean Abraham <seanabraham@chromium.org>
Commit-Queue: Sean Abraham <seanabraham@chromium.org>
Tested-by: Sean Abraham <seanabraham@chromium.org>
4 files changed
tree: ce2373afb37e8043fcf8bb929aff7dfacd8e13d5
  1. .gitignore
  2. LICENSE
  3. OWNERS
  4. cipd.yaml
  5. deploy_cipd.json
  6. deploy_cipd.sh
  7. src/