Merge multiversion binary download scripts

Currently, Evergreen uses some python code in evergreen.yml to find and download the appropriate binaries to run the multiversion test suites. Locally, engineers have historically used similar, but not identical, python code in setup_multiversion_mongodb.py to accomplish the same task. It would be good to try to merge these two codes in a way that allows engineers to run the same code that Evergreen uses; currently, there is nothing automated to remind us to make changes to setup_multiversion_mongodb.py when it breaks for local use.