LU-3536 osd: allocate it for each iteration.

LU-3536 osd: allocate it for each iteration.

Add osd iteration structure(osd_it_ea) to specific SLAB,
and allocate new osd_it_ea for each iteration, so iteration
can be nested, which will help DNE and LFSCK.

Since iteration for iam and quota are not so often,
we just allocate them with normal OBD_ALLOC_PTR.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: I6402259708264f9341f314e7a2f6afe16cc66481
Reviewed-on: http://review.whamcloud.com/13223
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>