LU-2492 obdclass: lu_object_find_at() waits forever

LU-2492 obdclass: lu_object_find_at() waits forever

In htable_lookup(), cfs_hash_bd_lookup_locked() could add an object
refcount and it messes with lu_object_put(), and the object's supposed
last holder will miss the change to free the object, leaving an 0
referred object in the hash table, and keeps lu_object_find_at()
waiting forever.

In this patch, we do not take the refcount of the dying object
in htable_lookup().

Signed-off-by: Bobi Jam <bobijam.xu@intel.com>
Change-Id: I4bd57e944bf9167d70d97845be55241b538872df
Reviewed-on: http://review.whamcloud.com/3439
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Hudson
Reviewed-by: Liang Zhen <liang@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>