feat(router): add optional controller SSL support

Testing this, you'll have to uninstall the routers entirely as the fleet unit has been updated to expose port 443:

```
$ deisctl uninstall router@1 router@2 router@3
$ deisctl install router@1 router@2 router@3
$ deisctl start router@1 router@2 router@3
```

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.