Bug#228984: uses apt-install too early

[Petter Reinholdtsen <pere@hungry.com>]

[Matt Kraai]
> hw-detect-full tries to use apt-install to install hotplug in its
> postinst, which fails because /target/etc/apt/sources.list does not
> yet exist.

If this fail, it must be an error in apt-install from rootskel, as
apt-install is supposed to store the list of packages to install in
/var/lib/apt-install/queue until /target/ is ready to be populated,
and base-installer is supposed to install the packages listed in the
queue when /target is populatet.