Oslo's logging code has some useful support for including bits of the
request context in log messages. While this isn't exclusively about the
request context in a dispatching RPC method, it seems useful for
oslo.messaging to support the concept for at least this use case simply
by recording the context in a thread local store before dispatching an
endpoint method and immediately clearing it when the method returns.
Note, we don't need to store weak refs in our store because we will
clear the reference in all cases rather than ever leaving a stale
reference around in the store.
Change-Id: I70ac06ed3a2a891a7a7b388b1823a0f3b08f2dd1
f1612f2895