Bug#867232: debian-installer: Does not ask for network mirror when installing from DLBD image

["M. Buecher" <maddes+debian@maddes.net>]

Package: debian-installer
Version: Debian 9.0.0 Stretch DLBD #1
Severity: important
Tags: d-i

Dear Maintainer,

when installing Debian from a DLBD image, then debian-installer does not
ask if a network mirror should be used, leaving /etc/apt/sources.list only
populated with the security repository and missing the standard and
stretch-update repositories.

I would expect to be asked for a network error, as it is when using a DVD
image, so that the normal and stretch-update repositories are correctly
set up in /etc/apt/sources.list.

-- System Information:
Debian Release: 9.0
  APT prefers stable
  APT policy: (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.9.0-3-amd64 (SMP w/1 CPU core)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US:en (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)