It should be possible to silence migration logs

[pcdavid]

Several migration participants log messages (as INFO) to inform about the model changes they perform. It's a good thing, but in the context of automated tests this produces a lot of noise in the logs.

We want to keep the automated tests applying migrations on old data models (instead of updating the models by doing a mass migration to the current Sirius version): it's a cheap way of testing the migrations themselves and ensuring, via our tests, that we can still load older Sirius models corectly.

At least in the context of tests however, it would be nice to be able to set a system property and disable these logs.