Make ./runtest --dump-logs dump logs for timeout tests's servers (#2412)

Kill the servers first, then kill the test clients, so that we can dump
logs for timeout tests's servers easily.
Note: Technically, we need to wait a while after killing the servers.
But in practice I think it's enough now.

Signed-off-by: yzc-yzc <[email protected]>

Author: yzc-yzc

tests/test_helper.tcl

@@ -408,8 +408,8 @@ proc test_server_cron {} {
             }
         }
         show_clients_state
-        kill_clients
         force_kill_all_servers
+        kill_clients
         the_end
     }