LU-744 osc: add lru pages management - new RPC

LU-744 osc: add lru pages management - new RPC

Add a cache management at OSC layer, this way we can control how much
memory can be used to cache lustre pages and avoid complex solution
as what we did in b1_8.

In this patch, admins can set how much memory will be used for caching
Lustre pages per file system. A self-adapative algorithm is used to
balance those budget among OSCs.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: I76c840aef5ca9a3a4619f06fcaee7de7f95b05f5
Reviewed-on: http://review.whamcloud.com/2514
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>