Chapter 9 (DigitalOcean Provisioner): add_hosts task fails due to changes in the DO API

In Chapter 9 when setting up the digital ocean provisioner I ran into an issues with the task "Add DigitalOcean hosts to inventory groups." because the jinja template `"{{ item.1.data.ip_address }}"` was failing to return the ip of the droplet.

It turns out this is because DO has changed their api a little bit and now returns a `networks` dict. See the stripped example json below

```json
{
"created_droplets": {
"results": [
{
"data": {
"droplet": {
"name": "a4d.lamp.varnish",
"networks": {
"v4": [
{
"gateway": "yyy.yyy.yyy.yyy",
"ip_address": "yyy.yyy.yyy.yyy",
"netmask": "255.255.240.0",
"type": "private"
},
{
"gateway": "xxx.xxx.xxx.xxx",
"ip_address": "xxx.xxx.xxx.xxx",
"netmask": "255.255.240.0",
"type": "public"
}
],
"v6": []
}
}
}
}
]
}
}
```

I did some digging and came up with the following.

```yaml
- name: Add DO Hosts to inventory groups
add_host:
name: "{{ (item.1.data.droplet.networks.v4 | selectattr('type', 'equalto', 'public') | first).ip_address }}"
```

Edit: I found #457 after making this and it looks like the solution there is more complete and it is indeed not fixed in version 1.14.

Start with Chapter 9's DigitalOcean provisioner and the “Add DigitalOcean hosts to inventory groups” task; compare it with the more complete solution in issue #457. Confirm the task follows the current networks.v4 public-address shape and verify the chapter's provisioning example.

Written by the indexing model from the issue text.