Implement a new function GETNODEMAP in libctdb.

Implement a new function GETNODEMAP in libctdb.
This function returns a pointer to a nodemap structure.

The returned structure must later be freed by calling ctdb_free_nodemap().

Move the definition of ctdb_sock_addr from ctdb_client.h to ctdb_protocol.h

Move the definition of the node flags, ctdb_node_and_flags and ctdb_node_map from ctdb_private.h to ctdb_protocol.h

Add both sync and async example for ctdb_getnodemap to the test application libctdb/tst.c