[recipes] replace the variable ${platform} with resolved-platform in test output
[recipes] replace the variable ${platform} with resolved-platform in test output

The intention is to create parity with cipd module[1] in recipe engine so that
there will be less friction when downstream repo starts to consume cipd module in
recipe engine

[1]: https://chromium.googlesource.com/infra/luci/recipes-py/+/refs/heads/master/recipe_modules/cipd/test_api.py#23

R=iannucci

Bug: 875523
Change-Id: I5f9100a81e7ca3c7300ab3b0ba198120d598ca48
Recipe-Nontrivial-Roll: build
Recipe-Nontrivial-Roll: infra
Recipe-Nontrivial-Roll: build_limited_scripts_slave
Recipe-Nontrivial-Roll: release_scripts
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1951224
Auto-Submit: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>
Commit-Queue: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools