Follows the same pattern as PerformJoin on roomserver (no error return).
Also return the right format for incompatible room version errors.
Makes a bunch of tests pass!
* Add PerformJoin template
* Try roomserver perform join
* Send correct server name to FS API
* Pass through content, try to handle multiple server names
* Fix local server checks
* Don't refer to non-existent error
* Add directory lookups of aliases
* Remove unneeded parameters
* Don't repeat join events into the roomserver
* Unmarshal the content, that would help
* Check if the user is already in the room in the fedeationapi too
* Return incompatible room version error
* Use Membership, don't try more servers than needed
* Review comments, make FS API take list of servernames, dedupe them, break out of loop properly on success
* Tweaks
* Add room version into createRoomReq
* Extract room version from m.room.create event when persisting
* Reduce cyclomatic complexity
* Update whitelist, gomatrixserverlib, tweaks to roomserver
* Update sytest-whitelist again
