Work osx

Hi @jvennix-r7, 

This pull request mainly switches from cmd_exec to session.shell_command_token on do_cleanup_once. The reason of  doing that is which the cmd_exec doesn't allow to pass a session, and the cleanup is always being done in the original unprivileged session. Which isn't the intended case for the on_new_session callback.

On the other hand, in this way the cleanup can be done without sending the sudoed payload to the background.