LU-13733 llite: report client stats sumsq

Commit cd8fb tries to account sumsq for every client operation, but
lprocfs_counter_init() did not init them properly, also add a test
case to verify new format of client stats.

Fixes: cd8fb1e8d300 ("LU-13597 ofd: add more information to job_stats")
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Change-Id: I4c7fc4c3958fdab757a9755cc851836971a4b700
Reviewed-on: https://review.whamcloud.com/39223
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Emoly Liu <emoly@whamcloud.com>
Reviewed-by: Patrick Farrell <farr0186@gmail.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>