Fixed temp URL breakage in Swift

* The API behavior is not well-documented in that it wants the HMAC
  to use the unencoded object name. CloudFiles had this same issue.

bug: 59894
Change-Id: I3f0c80eed55991bb85d0c12f98927efa19af6760
(cherry picked from commit c00ab2af44e004865b020fb4fba799ae898032e2)