Having trouble diagnosing a test failure.

waitForAllEarlierOplogWritesToBeVisible() has an invariant check that there is no open txn on the storage engine when it begins to wait (so it can see the latest oplog entries).

Changes:

• Add the RecoveryUnit's _state via toString(getState())
• Add the readConcern setting – UPDATE: doesn't seem worthwhile to link read concern files into the WT integration layer b/c no AutoGetColl* is taken so no read source selection occurs w/ possible snapshot opening
• Is there any way to add whether it's part of a multi-document transaction??