Improve bootstrap universe

[AurelienFT]

In the revamp of bootstrap tests we added tests universe for client and server that allow to test a bootstrap with determined data at the start of the test.

Currently, the determined data setup doesn't allow us to setup a way to stream changes. It should be possible to test more complex tests like before but needs a bit of design. One solution that I had is to make a list of changes at start and each time the final_state mock give the database reference it wait for a slot to happens and edit the database to generate changes. I don't know if it's the best solution or if it's possible so it's just a proposition.

Another point is to improve the checks at the end of the tests in the bootstrap in the bootstrap. As we are not building a second GlobalBootstrapState we need to make the checks of the fields directly in the universe. That should be straightforward