In the "rrsetorder" system test, the ns2 named instance is restarted
without passing the --restart option to bin/tests/system/start.pl. This
causes the log file for that named instance to be needlessly truncated.
Prevent this from happening by restarting the affected named instance
in the same way as all the other named instances used in system tests.
(cherry picked from commit 9146b956ae)