[Jepsen] Investigate Linearizability failure in ephemeral hard failover test

Linearizability failure was found during kv-engine-mad-hatter-jepsen-nightly-567 while running test lein trampoline run test --nodes-file ./nodes --username root --password couchbase --workload=failover --failover-type=hard --recovery-type=delta --replicas=2 --no-autofailover --disrupt-count=1 --rate=0 --durability=0:100:0:0 --bucket-type=ephemeral --cas --enable-tcp-capture --hashdump --enable-memcached-debug-log-level --disable-out-of-order-execution --net-interface=eth0.

Given its a hard failover test its likely that we've just dropped down to sequential consistency. However, we need to verify this. Also worth noting that this is an ephemeral bucket.