Many of the unit tests in our codebase involve creating an HttpRequest

and setting state on it (like users, a LocalSite, or a

ResolverMatch), which is done through a RequestFactory. This

requires a lot of annoying, repeated code.
We also often need to create a ReviewRequestDraft, which is easier,

but still requires more setup than is generally required for our other

models.
This change introduces new helpers for both. create_http_request()

takes care of constructing the HttpRequest from the factory and

setting various properties on it. Down the road, this could be updated

to provide more capabilities like running middleware.
create_review_request_draft() is a simple wrapper around

ReviewRequestDraft.create(), which lets unit tests avoid the extra

import.
A few unit tests have been updated to use create_http_request(), to

ensure that everything works as expected.

Unit tests pass.
Made use of these new helpers in upcoming unit tests.