Review Board 4.0 introduced a new set of HTTP request/response classes

for hosting services, making it easier to maintain support for services

in a consistent way. This impacted the unit tests for CircleCI and

Travis CI, which were both trying to simulate an HTTP request by

overriding some HTTP methods on the GitHub HTTP client class.
While there were recent fixes to these tests specific to Review Board

3.0, they didn't fix Review Board 4.0. Initially, the problem was that

the HTTP headers simulated weren't being seen by the GitHub

implementation, since there were differences in casing between the

versions (or, more specifically, between Review Board 3.0 on Python 2

and Review Board 4.0 on Python 3).
/r/11199 addressed part of this by updating how HTTP headers are

normalized, and /r/11200 updated GitHub to use the new HTTP classes.

This test completes the work by updating these tests to return the

correct HostingServiceHTTPResponse class now expected by GitHub,

fixing the unit tests across all supported versions of both Python and

Review Board.

Unit tests pass on all supported versions of Review Board and Python.