Experiment: introducing random message delivery delay to produce "old-new inversions"

[hengxin]

Now there are many occurrences of concurrency patterns.
However, the "old-new inversions" are very very rare.

Old-new inversions is closely related to the order in which messages (for operations) are delivered at each replica node.

Therefore, I want to introduce random message delivery delay to produce more "old-new inversions".

[hengxin]

1. Check ONI in the presence of concurrency pattern instead of checking "overwritten value".
2. Send messages to a (random) majority of server replicas instead of sending to all and waiting for a majority of acks.