main: suppress info messages with -p option

Log (to stderr) only warnings and higher when printing the
configuration to suppress the "chronyd starting" message.

main.c

@@ -492,6 +492,7 @@ int main
         user_check = 0;
         nofork = 1;
         system_log = 0;
+        log_severity = LOGS_WARN;
         break;
       case 'P':
         sched_priority = parse_int_arg(optarg);