Correctly wait for rollback to complete in rollback_with_coalesced_txn_table_updates_during_oplog_application.js

When crashAfterRollbackTruncation is false, we didn't wait for rollback to begin, so it's possible that when calling awaitNodesAgreeOnPrimary(), secondary1 has not started rollback, but already saw the new primary, and thus awaitNodesAgreeOnPrimary() will not see the network exception, but after this, rollback starts and connection closed, so the replSetFreeze() command sees the network exception. We should wait for rollback to complete before stepping it up.