Use connection pool in sandbox uploader

I was having an issue doing uploads with berkshelf when having the ssl verify set to false. On an initial upload, it would error out:

```
Ridley::SandboxUploader crashed!
Faraday::Error::ConnectionFailed: SSL_connect returned=1 errno=0 state=SSLv3 read server certificate B: certificate verify failed
```

After digging around for a bit I found that the sandbox uploader is creating faraday instances, but it does not use any options that may have been specified for the connection (like ssl). I updated it to use the connection pool, instead of creating a new instance. If there is a reason for not using the connection pool, then the connection options just need to make their way to the new faraday instances.