fix(example): render nginx port to config

[thevilledev]

Contains three individual fixes:

1. Since feat(image): make Nginx TCP port configurable hello-container#3 the hello-container's sample nginx configuration file "index.conf" has been changed to a template. It is not a configuration file that works out of the box as something is expected to render the listening port into the configuration file. Due to this change the example code for a rolling update through the Ansible inventory plugin does not work.

This PR replaces the variable with a default port of 80, through a regexp match, and does not introduce any template rendering.

2. While at it I also fixed the README in the repo example. At the moment terraform output does not return a raw string, leading to other commands in the tutorial to fail.

$ curl $(terraform -chdir=resources output lb_url)
curl: (3) URL rejected: Bad hostname

This works after returning a raw string representation of the LB URL.

3. Upon successful ansible runs, the unarchive step does not overwrite existing files. Thus, changing the animal parameter from cow to tiger doesn't affect the files on disk. With this PR, the nginx content directory is cleaned up before unarchiving.