LU-169 lov: add lsm refcounting

LU-169 lov: add lsm refcounting

This patch adds a reference counter to the lsm structure.
Each time a lsm is used, a reference must be taken with lsm_get/addref
(lsm_addref() can be used when we already own a reference on the lsm).
This reference can be released via obd_free_memmd(). The lsm is freed
when the last reference is dropped.

This patch also moves lov_stripe_md into a private data of
lov_object.

Signed-off-by: Jacques-Charles Lafoucriere <jacques-charles.lafoucriere@cea.fr>
Signed-off-by: Jinshan Xiong <jinshan.xiong@whamcloud.com>
Change-Id: I156b4cc2dc82bb15ae8107cf9842f100048c03d4
Reviewed-on: http://review.whamcloud.com/1874
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Johann Lombardi <johann@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>