The old FakeHTTPResponse we're using in the tests is really basic and
lacks a lot of the information that is expected in a response from an
adapter. This is a hard problem that we've already solved in the
create_response function so use that to create a test response instead
of a custom solution here.
Change-Id: I2999c9c69b4e9ad895114fab8ae7f8ce275fa2a4
Closes-Bug: #1642697
81b72f4397