jsonrpc: Added 'getnodes' to list known nodes.

getnodes returns an object containing a single array of 'nodes'. Each
element contains the node's ID, its hostname and its port. If
unknown (because we haven't seen a node announcement yet) then the port
is 0 and the hostname is null.

daemon/jsonrpc.c

@@ -285,6 +285,7 @@ static const struct json_command *cmdlist[] = {
 	&getlog_command,
 	&connect_command,
 	&getpeers_command,
+	&getnodes_command,
 	&gethtlcs_command,
 	&close_command,
 	&newaddr_command,