Update to support .ssh/config

Openstack provider plugin (https://github.com/cloudbau/vagrant-openstack-plugin) was failing to check that a server was ready as, in my case, login requires .ssh/config (but the server was started, and I could '''vagrant ssh''' to it, so my .ssh/config was working). Changing this to true, so Net::SSH can see the .ssh/config resolved the issue.

Maybe there's a good reason for the '''false''' in there but I can't think of it right now, so have a PR :)