Fixes bug 1104708
There could be severe performance drop for swift is one disk of one
storage node is problematic due to the tragic state of async disk I/O.
This patch provided PUT timing per kB transfered (ms/kB) monitoring
support for each non-zero-byte request of each disk and report to
statsD for alert.
-adding "object-server.PUT.<device>.timing" metrics for object-server.
DocImpact.
Change-Id: Ie94bddad28e8be52e71683bf6c9db988664abe47