Reproducible Builds: keep entries order when gathering ScatterZipOutputStream content in ParallelScatterZipCreator

currently, zip files created using ParallelScatterZipCreator have random order.
This is causing issues when trying to do Reproducible Builds with Maven MNG-6276

Studying ParallelScatterZipCreator, entries are kept sorted in memory in futures list: instead of writing each full scatter in sequence, iterating over futures should permit to write each zip entry in original order, without changing the API or any performance of the gathering process