Speed up system tests

Created by: SkyToGround

Description of work

Maybe this was a bit of wast of time. On the other hand, I know some other people that I feel are wasting a bunch of time right now. 😃 In the end, this PR seems to remove ~10 minutes from running the system tests on the first run and likely a few more minutes on subsequent runs on the same build node.

@matthew-d-jones I changed back to using Ubuntu as a base image (away from Alpine) due to Ubuntu not requiring us to build boost_build and flatbuffers.