feat(router): add optional controller SSL support

Testing this:

```
$ make -C router deploy
```

At this point, the router should be running and receiving HTTP requests.

```
$ deisctl config router set sslCert="$(cat deis.cert)"
$ deisctl config router set sslKey="$(cat deis.key)"
```

You should then be able to connect to the router via HTTPS. All HTTP connections will see the default "welcome to nginx!" page.
Could we also enable spdy? `listen 443 ssl spdy;` It's included in nginx since 1.4 and its recommended by h5bp https://github.com/h5bp/server-configs-nginx/blob/master/sites-available/ssl.example.com#L20