Proxy-server now requires Content-Length in the response header
when getting object and does not support chunked transferring with
"Transfer-Encoding: chunked"
This doesn't matter in normal swift, but prohibits us from putting
any middelwares to execute something like streaming processing of
objects, which can't calculate the length of their response body
before they start to send their response.
Change-Id: I60fc6c86338d734e39b7e5f1e48a2647995045ef