Allow to debug test failures

[Kaliumhexacyanoferrat]

As a developer of the GenHTTP web server, I would like to know why the server responds with unexpected status codes in some test runs (aka flaky tests), so I can make the stable again.

Example

Instead of ...

Assert.AreEqual(HttpStatusCode.OK, response.StatusCode);

do something like:

response.AssertStatus(HttpStatus.OK);

where AssertStatus is an extension method situated in the acceptance testing project which will print the request body in case of an unexpected status.

Acceptance criteria

• All places have been changed to the new mechanism
• The mechanism uses the preferred way to print the response content so it can be seen both in the test explorer as well as in the CI build