Add create_node_DEFAULT, no more hack_nodes_functions

Add create_node_DEFAULT, no more hack_nodes_functions

Reduce the amount of work needed to define how to create a new node
type.

* Each node type definition needs to define node_name_format_<TYPE>()

* Node types that should be part of the CTDB cluster should define
  node_is_ctdb_node_<TYPE>() and have it echo 1

* Nodes need not define create_node_<TYPE>() if they don't do anything
  unusual.

Signed-off-by: Martin Schwenke <martin@meltin.net>