Support multiple APP_HOST and APP_PORT

In my codeception setup, I have different suites running for various subdomains. As such, I need the ability to forward multiple hostnames. This patch will make it possible to pass in multiple hostnames as well as multiple ports, like so: 

`docker run -it -p 4444:4444 -e APP_HOST=host1,host2,host3 -e APP_PORT=8080,8888 davert/selenium-env`


EDIT: oh, this also includes the fix from #2