Updated installation images 2019-01-26 missing debian-ports-archive-keyring

[Frank Scheiner <frank.scheiner@web.de>]

Hi,

I just wanted to give the ISO for powerpc from 2019-01-26 a try, but it
looks like it is missing the `debian-ports-archive-keyring` package.

The UI (in normal installation mode) reports a deboostrap error during
"Install the base system":

```
The following error occured:

Couldn't find these debs: debian-ports-archive-keyring

Check /var/log/syslog or see virtual console 4 for the details.
```

The actual command that produces this result seems to be:

```
/usr/sbin/debootstrap \
--components=main \
--debian-installer \
--resolve-deps \
--include=debian-ports-archive-keyring \
--no-check-gpg \
sid \
/target \
file:///cdrom/
```

Both pool directory trees on the ISO are missing a
`main/d/debian-ports-archive-keyring` directory.

Cheers,
Frank