LU-4976 osp: add comments for osp_trans.c functions

LU-4976 osp: add comments for osp_trans.c functions

1) Rename some structures and functions names to avoid misguiding
   others, including:
1.1) osp_async_update_interpterer_t => osp_async_request_interpreter_t
1.2) osp_insert_async_update => osp_insert_async_request
1.3) osp_unplug_async_update => osp_unplug_async_request
1.4) osp_async_update_item => osp_async_request
1.5) osp_async_update_item_init => osp_async_request_init
1.6) osp_async_update_item_fini => osp_async_request_fini
1.7) osp_insert_async_update => osp_insert_async_request

2) Add introductory comment block for the osp_trans.c file. And add
   function comment blocks to all functions in the osp_trans.c file.

3) Typo fixing and code cleanup.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I3dc4e9d6613baa035d228f2254306b6a71b2d48c
Reviewed-on: http://review.whamcloud.com/10361
Reviewed-by: Richard Henwood <richard.henwood@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>