LU-4976 osp: add comment to osp_dev.c

LU-4976 osp: add comment to osp_dev.c

1. Add comments to each function in osp_dev.c.
2. remove unnecessary rc in osp_recovery_complete.
3. remove unnecessary LASSERTF in osp_device_fini.
4. rename some single character variable name to more
   meaningful name, like m-->osp, l-->ld etc
5. rename osp_find_or_create to osp_find_or_create_local_file
   to indicate it is actually for finding or creating a local
   file.
Signed-off-by: wang di <di.wang@intel.com>
Change-Id: Ia9ca565818aa6fc6f9ff932c371d9150e926fb60
Reviewed-on: http://review.whamcloud.com/10502
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Ned Bass <bass6@llnl.gov>
Reviewed-by: Richard Henwood <richard.henwood@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>