Wip rados whereis cmd

This pull request includes/is based on https://github.com/ceph/ceph/pull/2729

It uses the RadosWhereis class to implement "rados whereis <obj> [--dns]"

It exposes the new Formatter class "--format=table" "--format=table-kv" from pull request 
https://github.com/ceph/ceph/pull/2728