1) remove excess buckets (cmtruncjob with size=0 is the same as remove a bucket)
2) mismatch size of a bucket - generally after rolling restart / shutdown of a peer where the streaming connection of a hot buckett isnt consistent across the indexers - in which case we truncate to the smallest size of a bucket. we truncate to the smallest size because we dont ACK back to the forwarder until ALL copies of a hot bucket get a slice, so the assumption is that the the smallest size of the bucket has all the ACK'd slices (whereas the larger bucket has a piece that hasnt been ACKd)
