This should have better been done through some shared code
but it's not that obvious...

Fix stage2 meta-subprofile support while at that:
it was a questionable idea to use "/" as a delimiter
when part of the substitution is a pathname.

...and clarification (had to look up the prio list in apt sources).

install2 and live are both stage2 flavours, and I see no reason
rescue (the last one) should be any different here.

This one might probably change into core functionality but right now
it should help when you get not the branding, init system, or whatever
alternative you do _not_ need.

See-also: https://bugzilla.altlinux.org/show_bug.cgi?id=30806