Proxy Tests Could Use Improvement

[geemus]

We've had challenges figuring out an effective test setup for end-to-end testing of proxy settings and permutations, but it would be great to address this in more detail (and possibly move to rspec while we are at it).

In looking around some, I think WEBrick::HTTPProxyServer might be a promising candidate for an improved setup.

Some quick references for when I hopefully am able to return to this:

• https://docs.ruby-lang.org/en/2.2.0/WEBrick/HTTPProxyServer.html
• https://www.fedux.org/articles/2015/04/11/setup-a-proxy-with-ruby.html