Add support for creating a json output and additional tooling

[rn]

When running tests either repeatedly or the same tests on different system it is often useful to compare results. Currently, we store the test results in a csv file which is a ok, but a bit tedious to post-process in particular when trying to compare different results.

The proposal is to stash all the tests results as well as the system information and test meta data (such as start/end times etc) in a single json file with a reasonably well defined schema.

Once we have that we should be able to add simple tooling to read/compare multiple json files and generate, for example, a summary csv file from it.