Add e2e test for public IPs

Add an e2e test for public service IPs.
The IFS trick is cute but not great as it only works with a single character string...

In your comment you say:

```# Convert '1.2.3.4 5.6.7.8' => '"1.2.3.4", "5.6.7.8"'```

However it's actually converting it to `'"1.2.3.4","5.6.7.8"'` instead.

If you want to use a `join` then I suggest making it truly generic:

```shell
join() {
  local sep item
  sep=$1
  shift
  echo -n "$1"
  shift
  for item; do
    echo -n "${sep}${item}"
  done
  echo
}
```