Please detect libdvd-css failures

Originally created by @CyrilBrulebois on #11420 (Redmine)

While implementing support for snapshots, it was discovered that the initial patch series provided by intrigeri and me was missing support for a few cases in the apt-get wrapper (which makes it possible to keep track of all installed packages, so that they can be referenced in a manifest for snapshotting purposes).

Even though that was already fixed by intrigeri, it was considered bad taste to have a build go through while failures were supposed to be detected as early as possible.

I filed https://bugs.debian.org/824078 in the Debian BTS, but it seems the maintainer doesn’t quite get why the current behaviour is buggy and worth fixing.

Therefore, I suggest implementing checks in config/chroot_local-hooks/59-libdvd-pkg after those lines:

apt-get --yes install libdvd-pkg
dpkg-reconfigure libdvd-pkg

to make sure that the libdvdcss2 package is indeed installed at this stage.

Assigning to intrigeri as we discovered this together, so that he can comment on the issue.

Feature Branch: hybridwipe/feature/11420-verify-libdvdcss