LU-478 Set tunables on lvm device

LU-478 Set tunables on lvm device

- The set_blockdev_tunables() shouldn't chop the tail digit on
  the /dev/mapper/xxx device.
- Sometimes, the /sys/block/dm-x doesn't have the max_[hw]_sectors_kb,
  such errors should be tolerated.

Signed-off-by: Niu Yawei <niu@whamcloud.com>
Change-Id: I54c0e427772d8a1066a37d011d4cfd18240374b5
Reviewed-on: http://review.whamcloud.com/1046
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Bobi Jam <bobijam@whamcloud.com>
Reviewed-by: Yu Jian <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>