Implements configurable swift_owner_headers

These are headers that will be stripped unless the WSGI environment
contains a true value for 'swift_owner'. The exact definition of a
swift_owner is up to the auth system in use, but usually indicates
administrative responsibilities.

DocImpact

Change-Id: I972772fbbd235414e00130ca663428e8750cabca
Merge "Implements configurable swift_owner_headers"