Don't use requests.Response object directly

In requests 1.2 Responses are assumed to always have a HTTPResponse
object and it tries to extract headers from it. We solved this in the
create_response function but we didn't use it in all our tests.

Always use create_response when creating a custom matcher response.

Change-Id: I979f74a64c6f5accf1b88dcc3e5e004131945dff
Closes-Bug: #1361515