The function name setSystemOperationUnkillableByStepdown is not clearly expressing the exact case of killOp during stepdown. Like, the thread won't be interrupted during stepdown if it doesn't hold any global lock. 

We should add more comments around setSystemOperationUnkillableByStepdown so people who want to use it can make the right choice. We'd better provide suggestions on when a thread is interrupted by stepdown, how should the upper layer handle it.