Do not force UDF when mounting ISO files

For some reason, building with firmware="efi" produces *.iso files that
are actually iso9660 images, and not UDF. Let's rely on the kernel to
chose the right type.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Remove mdadm to resolve conflict

Newer mkinitrd from Kernel:stable conflicts with mdadm from 12.3. Remove
mdadm, since we do not need it currently.

Signed-off-by: Takashi Iwai <tiwai@suse.de>