Auto config node host and port for Selenium Grid

This will auto update the contents of the node config JSON and data string with the host and port of the Appium instance. This reduces the amount of things users have to setup in their node config JSONs.

Tested:
- With default port
- With custom port
- Restarting Selenium Grid while Appium was still running
- Restarting Appium while Selenium Grid was still running

Question:
- Is there any case where the node's URL won't be `localhost`?