fix swift middleware parsing

swift middleware is incorrectly stripping out 'HTTP_' headers. This
patch fixes this.

Change-Id: I866d08badd32c83f72f05d113acc684fc40c501d
Closes-Bug: #1394453
(cherry picked from commit 6417139b839dba96a6840c745d772e85a4f1d8bc)
Merge "fix swift middleware parsing" into stable/juno