This ticket was an action item identified from August 4th's 5.1 FCV Constants Retro: To always run the newest release binaries to prevent gaps that could allow breakages between the master branch and the latest release version branch.

Context:
We currently can't update multiversion tests after branching because theres no binary. If we update fcv somehow on the new branch and you update the binary as soon as the fcv update, then it doesn't matter if the binary is available on the just released branch, because they'll have the same history to go back and find the most recent commit on the branch to get that binary.

Implementation:

• Have the multiversion setup check the merge-base commit between a feature branch and master
• Download the newest commit on master proceeding the merge-base commit