Multiple (aggregated) tests.report are uploaded during a single build

[beatngu13]

Each time RecheckImpl#cap() is being invoked, we trigger CloudPersistence#save(...) and upload the aggregated tests.report to rehub. Suppose there are 10 tests classes, each consisting of 3 test methods. If cap() is called @AfterEach as usual, then we get 10 * 3 = 30 reports (all named tests.report) uploaded to rehub, although only the last one is interesting.

This is because we are not aware of when all tests have been finished. A simple solution could be to create some sort of ID (which is stable as long as the JVM lives, such as a static UUID) when the first test has been started and then send this as meta data.