libvirt-machine-properties: Offer to boot from CDROM/DVD

We have a "CD/DVD" option in "Devices & Shares" and that allows to
select a CD or DVD to be available inside the VM. It would be nice
being able to make this media bootable, in order to rescue a broken
system.

Fixes #34
4 jobs for allow-booting-from-cdrom in 63 minutes (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #324503
flatpak

00:53:40

 
  Review
passed #324504
review

00:02:42

manual #324505
allowed to fail manual
stop_review
 
  Cross Distro
passed #324506
fedora:rawhide

00:06:37