Add the elapsed time of VFS operations to the llite stats
counter, instead of just tracking the number of operations,
to allow tracking of operation round-trip latency.

Update sanity test_127[ab] to check that llite.*.stats and
osc.*.stats counter shows read/write stats in usec, and
fix code style nearby.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I40e188374f91c030d978a83157d8869e928cab07
Reviewed-on: https://review.whamcloud.com/36078


Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Li Xi <lixi@ddn.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>