Script to create existing test data based on SnPM13

[cmaumet]

This PR is open to suggest creating a script that would use latest SnPM13 to compute the test data rather than SnPM8. This would facilitate testing (no more manual ground truth data creation) but we have to be careful to only generate data for tests that have been first checked against SnPM8 (and are not created with the SnPM13 version we want to test!).