* Add support for reading `renderd.conf` to `render_expired`
* Add support for reading `renderd.conf` to `render_list`
* Add support for reading `renderd.conf` to `render_old`
* Add support for reading `renderd.conf` to `render_speedtest`
* Move renderd/render_* execution tests to own files
* Reduce variable scope & minor clean up
* Use `stat` rather than `access` to check if file exists