LU-1030 osc: move io data from lov_oinfo into osc_object

Cleanup the code and move io related data structure into osc_object
so that it will be easier to manage pages with red-black tree.

Signed-off-by: Jinshan Xiong <jinshan.xiong@whamcloud.com>
Change-Id: I7cd8d6278bb70b221351d9db4193c679f93aeb21
Reviewed-on: http://review.whamcloud.com/2009
Tested-by: Hudson
Reviewed-by: Johann Lombardi <johann@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>