When installing with ubiquity on a system which already had partitions it fails to pass the correct device info to grub which makes grub-install fail.

This does not happen on disks without partitions which is why we didn't see it in openqa. The test has no been adjusted to simulate this.

Easiest way to reproduce is to start with a fresh VM, install once, restart, try to install again (can use either complete wipe or resize option) --> ubiquity crashes at the end because pluginstall fails on grub-installer.
From journald it looks like one of the dev arguments isn't passed in correctly so grub-installer causes Wrong number of args: mapdevfs <path>.

https://bugs.kde.org/show_bug.cgi?id=398752

https://build.neon.kde.org/view/openqa%20%E2%9B%91/job/openqa_bionic_useredition_installation/57/