Ensure o.c.local is populated with the current Context

Since oslo.messaging was introduced, our logs at the server side of an RPC
call have not been receiving a context in order to inject user/tenant info
into the log format.

This is due to o.m implementing their own replacement for o.c.local, we
now need to manually populate o.c.local.

Additionally, remove some redundant code from the Context to_dict method

Change-Id: Id755c62681d425ae20473a57cf227a501b65b399
Closes-Bug: 1344040
Merge "Ensure o.c.local is populated with the current Context"