Use 2-level statistics to form global stats

[simmhan]

Buddy creates stats for its neighbors and itself. Passes intermediate stats to its buddy pool. O(mn + mb) messages instead of O(m) messages (m: # of peers, b: buddy pool size - 1; n: neighbor count).
This will require 1-level indirection to the buddy to decide the actual fog to hold replica. It will also make global stats more appox.