Add non-transactional afterClusterTime find to multi_statement_transaction_atomicity_isolation.js

afterClusterTime finds don't get killed automatically on stepdown or stepup. To make sure we don't deadlock, adding another state that just runs an afterClusterTime find would be useful. I'm not sure if there are any consistency checks we can add as well or anything we can expect from what the find returns, but just running the command may weed out deadlocks involving prepare conflicts outside of transactions.