[9.18] chg: test: Downgrade "timeout" and "attempts" arguments in shutdown
requested to merge backport-mnowak/shutdown-downgrade-timeout-and-attempts-arguments-9.18 into bind-9.18
The shutdown system test sends queries when named is shutting down, not in an attempt to get answers but to destabilize the server into a crash. With isctest.query.udp() defaulting to try up to ten times with a ten-second timeout to get a response we don't care about from a likely terminated server, we make the test run much longer than needed because of retries and long timeouts.
Also, see #4943 (closed).
Backport of MR !9507 (merged)