Build fails if `config/chroot_local-packages` contains packages

Originally created by @segfault on #15618 (Redmine)

• The problem
• Next steps

The problem

I tried this once with the packages I built for VeraCrypt (#15521 (closed)), and then again with an existing Debian package (https://packages.debian.org/stretch/amd64/vim/download). In both cases the build fails with:

P: Configuring file /etc/apt/sources.list
gpg: WARNING: unsafe permissions on homedir '/root/.gnupg'
gpg: keybox '/root/.gnupg/pubring.kbx' created
gpg: agent_genkey failed: Inappropriate ioctl for device
gpg: key generation failed: Inappropriate ioctl for device
cp: cannot create regular file 'cache/': Not a directory
P: Begin unmounting filesystems...

Next steps

For context, see live-build!1 (comment 184039).

• Prepare live-build fix (live-build!1 (merged))
• Add our live-build repo as a Git submodule of tails/tails, in some relevant place under vagrant/
• In the Vagrant box build process, somehow copy the relevant live-build files to the VM filesystem; this may boil down to running DESTDIR=something make install
• Prepare a MR against tails/tails that upgrades the live-build submodule to include live-build!1 (merged)
• Test
• Review
• Merge both live-build!1 (merged) and the MR against tails/tails