Let's ensure that make-initrd-luks gets to the base install
until installer is tweaked to enable in-flight installation
of options like this.

Adding luks to stage1 [make-initrd] features makes no sense
on the other hand (and it wasn't happening anyways due to
the lack of add_feature function call in config.mk as was
accidentally spotted).

And putting luks packages into an installer image lacking
the reference to alterator-luks isn't that sensible, let's
complain to logs at the very least (this isn't going to hit
the default output though).