Proxy support about go-getter

[mitchellh]

We do respect those. I tested to verify and got it to work locally:

$ http_proxy=http://127.0.0.1:8080 go-getter http://www.example.com/ foo
2016/06/13 10:34:45 Success!

And my proxy verifies it proxied the connection:

2016/06/13 10:34:45 [004] INFO: Got request / www.example.com GET http://www.example.com/
2016/06/13 10:34:45 [004] INFO: Sending request GET http://www.example.com/
2016/06/13 10:34:45 [004] INFO: Received response 200 OK
2016/06/13 10:34:45 [004] INFO: Copying response to client 200 OK [200]
2016/06/13 10:34:45 [004] INFO: Copied 1270 bytes to client error=<nil>

Unfortunately this looks like something else. Is Nomad perhaps removing these env vars?