We should do the following to improve the relevance of diagnostics we have in the face of data inconsistency issues:

1. Update ReplSetTest#stopSet() to call ReplSetTest#checkOplogs() in addition to ReplSetTest#checkReplicatedDataHashes(). Care should be taken to ensure that tests do not run significantly longer because they need to verify a large oplog when shutting down the replica set.
2. Update the PeriodicKillSecondaries hook to run the CheckReplOplogs hook in addition to the CheckReplDBHash and ValidateCollections hooks.

Original description

We now save all of the data files, but it would be great if the test could check the oplogs automatically and note any differences.