Do not use PID files for --run-service so one service can run concurrently.

bin/pt-agent

@@ -6065,7 +6065,7 @@ sub run_service {
 
    my $daemon = Daemon->new(
       daemonize      => 0,  # no need: we're running from cron
-      pid_file       => "$lib_dir/pids/$service.run",
+      # no pid_file because --run-service X must handle concurrent runs of X
       log_file       => "$lib_dir/logs/$service.run",
       force_log_file => 1,
    );