The first step here was taken at
https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/1371349
to dump the summary of the entire test run into the results directory.

I think we should also dump a summary of all non-empty sections that the checkpoints define. This allows for _much_ simpler data collection and reporting on a multitude of tests, regardless of what we do with the data on the dashboard.

There's a concern of course over adding too much data as the checkpoints, especially on PLT, are quite frequent, but while I think we should verify that this doesn't super blow up the results, it's more useful to have this data than not to.