The provisioning module knows more about how nova deals with IP
addresses now. Ensure that the inventory module is similarly as smart
by separating out the logic into the openstack/module_utils.

- auth_system
- region_name

These are config settings that could be left out in many scenarios, but
the current code is requiring them. With this in place, I can get by
with this minimal .ini file:

```ini
[openstack]
version=1.1
auth_url=http://{keystone_host}:5000/v2.0
project_id=web
username={username}
api_key={password}
```

@mpdehaan said that nothing uses them at
https://github.com/ansible/ansible/pull/7988#issuecomment-47600006

Signed-off-by: Hector Acosta <hector.acosta@gmail.com>