Use a doubled proxy-logging instead of each middleware handling it
differently (if at all)

Adding a swift.source to wsgi pre_auth funcs and all middleware that makes
subrequests to proxy server.

NOTE: This change will result in a change in the number of proxy logs made for
staticweb, formpost, tempurl, and any other middleware that performs sub
requests (including swauth and SOS).

Please see docs for details.

DocImpact

Change-Id: I80cf2806add1c3d34054147e2515944be340455b
Merge "Use a doubled proxy-logging instead of each middleware handling it differently (if at all)"