SSH agent forwarding for Docker and Vagrant

This addresses #587 

I've tried to create an issue in JIRA, but I can't seem to find the correct project (I don't appear to have visibility for `QENG`) ; any help would be much appreciated.
During my testing, I've seen this hash being passed to Net:SSH during connect, and as a result, the agent being forwarded. Without this change, the ssh session is established without agent forwarding enabled, and any connections that require authentication fail without a private key is present.