BookKeeper stats are not accurate

[shubhamtagra]

There are a few issues in bookKeeper stats:

1. Counters (totalRequests, etc) need to be made atomic. We need to study the impact of changing them to atomic before rolling out the change
2. Need to store how much did a node read in behalf of other node (via readData call)
3. Cache Hit/Miss stats do not account for non-local reads