This subprofile is akin to THE_* variables family: the configuration
bits and script hooks sitting there influence whatever chroot is
declared to be the user facing one in the end, whether it comes
from vm image or live subprofile.

The services feature ought to be a changeset of its own which would
be based on rootfs and become the base for ve/vm changes but I chose
to just do it atomically; some pre-existing duplicates are pruned now.