wip 9979 (proxy read support)

Add proxy read support

Signed-off-by: Zhiqiang Wang <zhiqiang.wang@intel.com>
You are right. Since we don't have async promotion yet, how do you think we add this pull request as a 'read proxy' cache mode (like read forward) first? When later we add the async promotion, we can move this to the writeback mode, and kick off promotion if needed.