Bug#855035: debian-installer: https does not work with stretch rc2 installer

[Hilko Bengen <bengen@debian.org>]

Package: debian-installer
Severity: normal

Dear Maintainers,

while working to build a more automated installation process around d-i
Stretch RC 2 (using the netinst iso), I tried to preseed the following:

,----
| choose-mirror-bin     mirror/protocol   select  https
| choose-mirror-bin     mirror/https/hostname     string  deb.debian.org
| choose-mirror-bin     mirror/https/directory    string  /debian
`----

This does not work as I expected: According to the log, fetching the
Release files using wget seems to work, but the in-target apt emits the
following:

,----
| Reading package lists...
| 
| E: The method driver /usr/lib/apt/methods/https could not be found.
| E: Failed to fetch https://deb.debian.org/debian/dists/stretch/InRelease
| E: Some index files failed to download. They have been ignored or old
| ones used instead.
`----

I guess that adding apt-transport-https to the base system (and
including it in the netinst .ISO) ought to fix this problem.

Cheers,
-Hilko