BSN: Add context to backend request for debugging

Include the request context with calls to the backend
Big Switch controllers to assist with event correlation
and debugging object provenance. The auth token is
stripped since this information is sensitive and
these requests will appear in debug logs.

This also removes mutable objects from default arguments
in some of the server manager function definitions that
were interferring with the new use of the headers dict.

Closes-Bug: #1364696
Change-Id: I5b80b1596cc145742457b3603cbcd67f6e0d9f36
Merge "BSN: Add context to backend request for debugging"