Apply an HTTP_PROXY for us corporate shills.

[johnbellone]

This helps all of us that are stuck in the corporate world. Use upstart to export an HTTP_PROXY which is specified through the configuration.

[johnbellone]

I read the Upstart documentation and it seems both env and export could have been used here. It should be noted that sudo would reset the environment if we ever performed that here. The documentation that I followed for upstart configuration.

[bflad]

This looks good to me. Thanks for the contribution! I'll also create a node['docker']['http_proxy'] default attribute that is nil and bump the version.