LU-10607 osd-zfs: skip io stat for OI scrub

LU-10607 osd-zfs: skip io stat for OI scrub

It is unnecessary to stat io for OI scrub triggered request.
On the other hand, the OI setup logic may read/write the OI
scrub file. At that time, related lproc (including io stat)
for such OSD is not initialized yet. So this patch skips io
stat for OI scrub.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I9498c1351c1875ac9aa46eed5189cb61a6d102ac
Reviewed-on: https://review.whamcloud.com/31180
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>