Currently, replica_sets_multiversion and sharding_multiversion will use the useRandomBinVersionsWithinReplicaSet test option to randomize the binary versions used in each test. Initially, we only had testing between lastLTS and latest versions, so ReplSetTest would always default to set lastLTS as the FCV if the option is passed in. However, PM-1803 introduced testing between last-continuous and latest versions, which means we need to update the test infrastructure to also check the value being passed into the option.