KeenQueryTestBase lower-level HTTP Request validation

[masojus]

We should work on making it easier to do lower-level validation of HTTP requests in the query tests. KeenQueryTestBase might be a good place to share this functionality since this is where we have the shared code to mock and capture requests and responses.

From PR #96:

    // TODO : Add a means to check more about the lower-level HTTP request, like the specific
    // headers, URL, response codes, etc. Both the DELETE and GET requests have no request body
    // so everything is in the URL/headers. KeenQueryTest does this in some places.

...and...

    // TODO : We should add some verification of the actual URL produced in the Request
    // the way we do in some of the tests in KeenQueryTest.