Currently, statistics are organized by command. However, it would also be
useful to display statistics organized by policy. Different policies may be
based on different storage properties (ie, faster disks).
With this change, all the statistics for object timers will be sent per policy
as well.
Policy statistics reporting will use policy index and the name in Graphite will
show as proxy-server.object.policy.<policy-index>.<verb>, etc.
Updated unit tests for per-policy stat reporting and added new unit tests for
invalid cases.
Updated documentation in the Administrator's Guide to reflect this new
aggregation.
Change-Id: Id70491e4833791a3fb8ff385953d69018514cd9c
4765189ef3