The issue actually hit image.in/Makefile: "metadata" target
in features.in/metadata/lib/50-metadata.mk wasn't reached
even if features.in/build-distro/lib/90-build-distro.mk
would ACK that the "whatever" actions included "metadata";
thus Metadata/pkg-groups.tar wasn't created and the installer
silently failed to install the .base system.

Let's armour the rest of the cases where the order of inclusion
might be important as well.