Reconfigure bootstrapped packages after preseeding.

@hertzog found this while working on https://salsa.debian.org/debian/iproute2/merge_requests/1 Given iproute2 is in the debootstrap list, the preseed wasn't working given it runs after the bootstrap (it has to). This fix runs dpkg-reconfigure if it finds that the package mentioned in a preseed file was already installed, which means it was part of the bootstrap phase.

I've tested this with iproute2 and it seems to work fine.

Would you like this behaviour to be disabled by default and behind a flag?

Also fix a Lintian Error introduced in a previous commit (not yet released).