daemon: add dev-routefail command.

We're about to change the code so that if it can't route, it will fail
the HTLC.  The current low-level tests will hate this, so have a dev switch
to turn that off.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

daemon/jsonrpc.c

@@ -265,6 +265,7 @@ static const struct json_command *cmdlist[] = {
 	&signcommit_command,
 	&output_command,
 	&add_route_command,
+	&routefail_command,
 };
 
 static void json_help(struct command *cmd,