Remove Vagrant cache-mechanism from build configuration as it might break on some filesystems

on some filesystems (i.e. zfs) its only possible to build tails with the libvirt cache attribute set to ‘writethrough’ instead of ‘none’ in the Vagrantfile. i guess thats a corner case, but maybe that should be configurable via env.

Feature Branch: bugfix/14404-remove-vagrant-disk-cache-setting

Related issues

Blocks #15334 (closed)

Original created by @muri on 14404 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information