Once SERVER-26264 is complete, a 3.2 mongos process will quickly exit with an error status if you point it at 3.4 config servers with featureCompatibilityVersion "3.4". We should write a test in the multiVersion suite to verify this behavior. The test should perform the following steps:

1. Start an all 3.4 sharded cluster.
2. Verify that the feature compatibility version is "3.4".
3. Assert that a new 3.2 mongos fails to start up when joining the cluster.
4. Set the feature compatibility version to "3.2".
5. Assert that a 3.2 mongos can now start up against the cluster and can perform reads and writes to the shards.