More preparatory refactoring of the OidcHandler tests

Remove `Request` return value from `make_request`

It used to write an empty file if you gave it a -o arg.

... so that we can test its behaviour when it raises.

Also pull it out to the top level so that I can use it from other test classes.

The tests that need this all do it already.

despite the warnings saying "don't implement get_extra_attributes", we had
implemented it, so the tests weren't doing what we thought they were.

This was never used, so let's get rid of it.

this didn't seem to be doing a lot, so remove it.

The two are equivalent, but really we want to check the HTTP result that got
returned to the channel, not the code that the Request object *intended* to
return to the channel.

* move simple_async_mock to test_utils

... so that it can be re-used

* Remove references to `SamlHandler._map_saml_response_to_user` from tests

This method is going away, so we can no longer use it as a test point. Instead,
factor out a higher-level method which takes a SAML object, and verify correct
behaviour by mocking out `AuthHandler.complete_sso_login`.

* changelog

Removes faulty assertions and fixes the logic to ensure the max
stream token is always set.

* Remove references to handler._auth_handler

(and replace them with hs.get_auth_handler)

* Factor out a utility function for building Requests

* Remove mocks of `OidcHandler._map_userinfo_to_user`

This method is going away, so mocking it out is no longer a valid approach.

Instead, we mock out lower-level methods (eg _remote_id_from_userinfo), or
simply allow the regular implementation to proceed and update the expectations
accordingly.

* Remove references to `OidcHandler._map_userinfo_to_user` from tests

This method is going away, so we can no longer use it as a test point. Instead
we build mock "callback" requests which we pass into `handle_oidc_callback`,
and verify correct behaviour by mocking out `AuthHandler.complete_sso_login`.

Spam checker modules can now provide async methods. This is implemented
in a backwards-compatible manner.

Fixes #8846.

Fixes #8866

Fixes #8892

* Factor out _call_attribute_mapper and _register_mapped_user

This is mostly an attempt to simplify `get_mxid_from_sso`.

* Move mapping_lock down into SsoHandler.

this was using `canonical_json` without setting it, so when you used it as a
standalone class, you would get exceptions.

Deprecate both APIs in favour of the Delete Room API.

Related: #8663 and #8810

This defaults `ip_range_blacklist` to reserved IP ranges and also adds an
`ip_range_whitelist` setting to override it.

Related: #8810
Also a few small improvements.

Signed-off-by: Dirk Klimpel <dirk@klimpel.org>

Pin the docker version for multiarch builds

It seems that letting CircleCI use its default docker version (17.09.0-ce,
apparently) did not interact well with multiarch builds: in particular, we saw
weird effects where running an amd64 build at the same time as an arm64 build
caused the arm64 builds to fail with:

   Error while loading /usr/sbin/dpkg-deb: No such file or directory