Do not pollute t_server_null.sh logs with "ps" output

Signed-off-by: Samuli Seppänen <[email protected]>

tests/t_server_null_server.sh

@@ -74,7 +74,7 @@ do
     # Make sure that the server processes are truly dead before exiting
     while :
     do
-        ps -p $SERVER_PID || break
+        ps -p $SERVER_PID > /dev/null || break
         sleep 0.2
     done
 done