ansible/gen_certs: Fix regression when HTTP_PROXY is not set
ansible/gen_certs: Fix regression when HTTP_PROXY is not set

Regression from 46131210fc99fe84e121f24987f0c1669f277710 when
`http_proxy` is *not* defined.

Ansible tried to quote the undefined variable, and it ended up breaking like:

```
Could not resolve proxy: {# https_proxy #}; Name or service not known
```

cgwalters/kubernetes-contrib,cgwalters/kubernetes-contrib,cgwalters/kubernetes-contrib,cgwalters/kubernetes-contrib,cgwalters/kubernetes-contrib,cgwalters/kubernetes-contrib