The regression was introduced by commit
3c39b0b7 which makes it possible to
create working stretch containers by forcinig `init` to be in the
included package list.

However, `init` didn't exit before jessie, so now for wheezy we
explicitly include `sysvinit`; sysvinit on wheezy is essential,
so it would already be included anyway.
Signed-off-by: Antonio Terceiro <terceiro@debian.org>