Current install script only fills CN field with PUBLIC_HOST value. When
trying to access api and provide the self signed certificate to verify
server certificate, the request will fail with SSL:
CERTIFICATE_VERIFY_FAILED error.

To prevent this error, the install script should add "subjectAltName =
IP.1:${PUBLIC_HOST}" when generating self signed certificate.

```python
import requests
requests.get('https://${API_PREFIX}/access-keys',verify='shadowbox-selfsigned.crt')
```

Use a regex to test whether input hostname is an IP address. If it's an
IP address, use "IP" prefix. Otherwise, use "DNS".