use a blacklist instead of whitelist for disk devices, and refactor refresh_devices() method

[oliverkurth]

Fix for #23 , and refactor refactor refresh_devices() method. This now uses a list of devices to be excluded, instead if a list to be included. This allows for example virtio devices (253), but disallows for example floppy disks.

Also refactor to remove code duplication.

Tested by creating a custom iso with no kickstart (to allow interactive install) and installing in virt-manager.

Additionally, this includes example config files to create an ISO image. Instructions:

Prerequisites: docker with buildx plugin, a few GB of space (for docker images, package repository and ISO).

Steps:

• clone this project
• checkout this branch (git checkout topic/okurth/virtio)
• export POI_IMAGE=photon/installer
• build container image: cd docker && docker buildx build --build-context poi-helper=$(realpath ..) -t $POI_IMAGE .
• create a temporary repository in /root/repo (can be anywhere, but adjust paths in following commands):

cd examples/iso
docker run --rm --privileged -v/dev:/dev -v$(pwd):/workdir -v /root/repo/5.0:/repo $POI_IMAGE create-repo -c packages_installer_initrd.json
docker run --rm --privileged -v/dev:/dev -v$(pwd):/workdir -v /root/repo/5.0:/repo $POI_IMAGE create-repo -c minimal_ks.yaml

• finally, build the ISO: docker run --rm --privileged -v/dev:/dev -v$(pwd):/workdir -v /root/repo/5.0:/repo $POI_IMAGE photon-iso-builder -y iso.yaml
• you should now have a shiny ISO: photon-5.0.iso (or use -n <name> to set another name)

You need to be root for all of the above, or use sudo (I tested this in a throw-away VM).