Fix SLES 15 packaging

SLES 15 doesn't have any sort of init functions which is why the error is
converted to a status message. A dummy file that just prints an error is
placed into /etc/init.d/ to make it clear to the users that they should
use systemd to start MaxScale.

etc/fallback/maxscale.in

@@ -0,0 +1,4 @@
+#!/bin/sh
+
+echo "Init scripts are not supported on this platform, use either systemd or launch MaxScale manually"
+exit 1