code: def delete_persistent_data(role, zk_node):
      
      if role:
          destroy_volumes(role)
          unreserve_resources(role)
  
      if zk_node:
          delete_zk_node(zk_node)
docs: Deletes any persistent data associated with the specified role, and zk node.
  
          :param role: the mesos role to delete, or None to omit this
          :type role: str
          :param zk_node: the zookeeper node to be deleted, or None to skip this deletion
          :type zk_node: str