update to handystats v2

**DO NOT MERGE**

Request metrics collection mechanics is performed via request_wrapper.
Upload request instrumented.
Handystats' file_logger added ("stats-log" config section).

Collected metrics:

* mds.\<request\>
  -- rate for request (get, upload)

* mds.\<request\>.\<reply code group\>.time
  -- timings for reply code group (2xx, 3xx) of request (get, upload)
  -- 'frequency' statistic may be used for rps

* mds.\<request\>.reply.\<reply code | group\>
  -- rate for reply code or group (2xx, 404, etc.) of request (get, upload)