Add a test for `/make_knock` and `/send_knock` against a homeserver which is in the middle of a partial join.

[reivilibre]

Similar to #432 but for knocking.

Needs:

• Add a SendKnock method and RespSendKnock struct gomatrixserverlib#329
• Add a response type for make_knock gomatrixserverlib#328
• TODO MakeKnock fed client function