LU-4503 clio: lu_ref_del() mismatch ref add scope

LU-4503 clio: lu_ref_del() mismatch ref add scope

git commit 4fcbd1af9ec3b1e5f6424d925f43f0cb2910c3ec adds page to
a list and aggregate issuing them to writeback cache; A page add
is referenced in llite/vvp io scope, while writeback cache commit
de-refers it under osc sub io scope, and --enable-lu_ref will detect
this scope mismatch.

Signed-off-by: Bobi Jam <bobijam.xu@intel.com>
Change-Id: I368ac1f7118f420edde651ce84a595128d15b527
Reviewed-on: http://review.whamcloud.com/8970
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: frank zago <fzago@cray.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>