The feature officially introduces the "engineering passwords"
including empty ones which have been around since forever but
weren't properly managed (and still are not, at least until
there are no stray passwd/chpasswd/usermod calls in both the
profile, installer-features and all the other related parts).

It is based on an m-p-d init3-users script by stanv@ but was
cleaned up and restructured in a pretty severe manner; thanks
glebfm@ for additional discussion.

This also cleans up the kludge previously stuck into build-vm.

Note that vm/icewm sports graphical autologin now as well as
the default root password (which can be overridden by passing
ROOTPW=... to make but it is a change from the previous state
of affairs indeed).