This code brings the SimpleHttpClient into line with the
MatrixFederationHttpClient by having it raise HttpResponseExceptions when a
request fails (rather than trying to parse for matrix errors and maybe raising
MatrixCodeMessageException).
Then, whenever we were checking for MatrixCodeMessageException and turning them
into SynapseErrors, we now need to check for HttpResponseExceptions and call
to_synapse_error.
Adds a `.wrap` method to ResponseCache which wraps up the boilerplate of a
(get, set) pair, and then use it throughout the codebase.
This will be largely non-functional, but does include the following functional
changes:
* federation_server.on_context_state_request: drops use of _server_linearizer
which looked redundant and could cause incorrect cache misses by yielding
between the get and the set.
* RoomListHandler.get_remote_public_room_list(): fixes logcontext leaks
* the wrap function includes some logging. I'm hoping this won't be too noisy
on production.
