Adapt the test that was added in
mysql/mysql-server@6b65d9032cbb6c1016cb09d056df6885e3d25dc6
but omitted in commit 2e814d47.

Instead of triggering a log checkpoint, we will only trigger
a redo log flush before killing the server.
Note: the mtr.commit() call in trx_rollback_for_mysql()
will not actually make the undo log header page state change durable.
A call to log_write_up_to(mtr.commit_lsn(), true) would do that.

It is unclear what the originally reported bug scenario was.
As long as innobase_rollback_by_xid() will not return without
ensuring that the redo log has been durably written, we should be safe.