Previously, if a transaction failed with commit_unknown_result, and was
actually committed, it would look like data that magically appeared in the
database and verification would fail.
Now, we explicitly re-read and check to see if the commit happened, so that we
may maintain an accurate understanding of what the database state should be.
VersionStamp previously would range-read the entire database during validation.
This has the unfortunate effect of making it fail during validation if run with
any other workload that writes keys to the database.
Now, all keys written and read are done with a configurable prefix, so that it
may co-exist with a variety of other workloads.
Alex Miller