Use timeout for rndc status in shutdown test

Pass 5 second timeout to the rndc status command(s) to avoid hitting the
hard 10 second timeout from subprocess.call, which would result in an
unwanted exception that would only mask the real issue: if the rndc
status times out in this test, it is likely due to the server not
stopping as it should.

bin/tests/system/shutdown/tests_shutdown.py

@@ -105,7 +105,7 @@ def do_work(named_proc, resolver, rndc_cmd, kill_method, n_workers, n_queries):
             else:
                 # We attempt to send couple rndc commands while named is
                 # being shutdown
-                futures[executor.submit(launch_rndc, ["status"])] = "status"
+                futures[executor.submit(launch_rndc, ["-t", "5", "status"])] = "status"
 
         ret_code = -1
         for future in as_completed(futures):