Dropping httpbin requirement from tests.

[tomchristie]

We're currently using httpbin as a requirement in our test cases.

We could instead be working with something much slimmer here since all we actually want is, a background thread running...

• An open socket that's able to respond with an HTTP/1.1 hello world message.
• An SSL secured open socket that's able to respond with an HTTP/1.1 hello world message.

These could either be over the lifespan of a single test, over the lifespan of a test module, or over the lifespan of the suite. It probably doesn't matter too much which.

We could either do this from scratch with a low-level socket implementation, or we could lean on stdlib's built-in socketserver/http.server...

• https://gist.github.com/davidbgk/b10113c3779b8388e96e6d0c44e03a74
• https://www.piware.de/2011/01/creating-an-https-server-in-python/