Take down condition subsystem at shutdown/reboot

Leave the system as it was when we found it.  Also, we'll build things
on top of cond_is_available() to handle pre bootstrap and pre shutdown
tasks.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/sig.c

@@ -322,6 +322,9 @@ void do_shutdown(shutop_t op)
 	plugin_exit();
 	api_exit();
 
+	/* We can no longer act on conditions, activate script runner */
+	cond_exit();
+
 	/* Reap 'em */
 	while (waitpid(-1, NULL, WNOHANG) > 0)
 		;