LU-8791 osd-zfs: hold oo_guard read lock for object write

LU-8791 osd-zfs: hold oo_guard read lock for object write

In order to avoid the deadlock of changing object block size and
writing the object at the same time.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: Id1c3c7e66e74d4f61e2136311a0723b8da2da3bb
Reviewed-on: http://review.whamcloud.com/23550
Tested-by: Jenkins
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>