LU-7206 mdd: stop orphan cleanup before finish FLD

LU-7206 mdd: stop orphan cleanup before finish FLD

Stop orphan cleanup thread in PRE_CLEANUP phase.
Because orphan cleanup threads might need lookup
FLD, (__mdd_orphan_cleanup()->mdd_object_init()->
lod_object_alloc() ->lod_fld_lookup()), so let's
stop orphan cleanup threads before FLD cleanup.

Signed-off-by: Di Wang <di.wang@intel.com>
Change-Id: I8df9832c633017e2fca866579b497f8215054d31
Reviewed-on: http://review.whamcloud.com/23029
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>