Ceph

This ticket calls for the capability of radosgw-admin to delete bucket content without deleting the bucket itself. The existing command "bucket rm" does both. However, after the introduction of multisite sync policy feature, it is now possible to store bucket content in some zones but not in some others within the same zonegroup. To help facilitate the migration of bucket content within the zonegroup, it would be helpful if we can purge bucket content in one zone after it has been sync-ed over to a different zone, thus achieve the purpose of migration.