This PR fixes
- close leaking bandwidth report channel leakage
- remove the closer requirement for bandwidth monitor
instead if Read() fails remember the error and return
error for all subsequent reads.
- use locking for usage-cache.bin updates, with inline
data we cannot afford to have concurrent writes to
usage-cache.bin corrupting xl.meta
This change tracks bandwidth for a bucket and object
- [x] Add Admin API
- [x] Add Peer API
- [x] Add BW throttling
- [x] Admin APIs to set replication limit
- [x] Admin APIs for fetch bandwidth