As the server code keeps evolving, there may be any number of operations started by the primary when it steps up. no_disconnect_on_stepdown.js was written under the assumption that there weren't any operations started by the primary itself.

In this test, we
1) step up a primary
2) issue a write that hangs
3) step down the primary
4) assert that exactly one operation was killed

The assertion breaks if the primary itself launched a few operations on step up. When that's the case, we may kill more than one operation.

We can change the assertion to be "at least one operation is killed" and we can make sure the operation was killed with the right error code.