This is follow-on work for
SERVER-36982 and SERVER-37227. We disabled the dbhash background thread for enableMajorityReadConcern:false, since the thread performs a majority afterClusterTime read, in order to check that the secondary has applied up to the chosen cluster time and advanced its majority commit point. Instead, we can run replSetGetStatus in an assert.soon() loop and check the lastCommittedOpTime.
We plan to disable atClusterTime with enableMajorityReadConcern:false, since we aggressively forget history, but we can leave it on when test commands are enabled. The dbhash background thread uses the WTPreserveSnapshotHistoryIndefinitely failpoint to ensure history is preserved.