Add support for http_proxy at remote server

[hoanghuynh]

My remote server needs to use an http_proxy/https_proxy to download packages from internet. Can you add support for this? Usually I would add export http_proxy=someproxy:port and export https_proxy=someproxy:port to the beginning of my script.

Even better, can we have an option to run some commands (like the exports above) before sshcode starts executing?

[sreya]

This is similar to #73 ...would downloading it locally and scp'ing it to the server suffice? The only downside I see is that it could be potentially be quite slow depending on your network speed