Profiles from parent POM are injected multiple times if parent is part of reactor build

The test project provided for MNG-4022 depends on a bug in the project builder to trigger to actual Xpp3Dom merging issue. When the parent POM is part of the reactor, it will be added to the project cache and its model already includes active profiles. When the child is build next it retrieves the previously created parent model from the cache to assemble the lineage and injects the active profiles again. This causes discrepancies in the effective model if profile injection has additive effects on the model.