Provide a public API to get cache instances within a cluster

Hello @nicks, @dpup, 

Please review the following commits I made in branch 'xiao-add-api-to-servers'.

7aa84cb52cfb10715e4a1582ff3caa0f5c316830 (2014-01-27 15:55:25 -0800)
Provide a public API to get cache instances within a cluster

R=@nicks
R=@dpup