LU-13597 ofd: add more information to job_stats

LU-13597 ofd: add more information to job_stats

Request processing times/latency and basic IO size information
is added to the job_stats output. This allows monitoring per-job
request processing performance.
Except read_bytes and write_bytes in bytes units, all the others
use "usecs" units and show min/max/sum values. What's more, two
new counters for read and write time are added to calculate
bandwidth. The output format is like:
write_bytes: { samples: 1, unit: bytes, min: x, max: x, sum: x,
sumsq: x}

sanity.sh test_205b is modified to verify this patch.

Signed-off-by: Emoly Liu <emoly@whamcloud.com>
Change-Id: I7a5b77ca0ba464f6330a4bc56735c7762e167019
Reviewed-on: https://review.whamcloud.com/38816
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>