LU-1303 lod: functions to manipulate sub-devices

lod needs to be connected directly to all OST. configuration
subsystem brings OSP for every OST in the cluster, then
LOD connects to them and use.

the patch fixes cfs_foreach_bit() so that it continues scan
from the next bit.

Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Change-Id: I6a8b98ed8964fba1410552c94c408b004eae00a4
Reviewed-on: http://review.whamcloud.com/4048
Tested-by: Hudson
Reviewed-by: wangdi <di.wang@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>