qemu: Replace usb-storage with usb-bot

qemu: Replace usb-storage with usb-bot

usb-storage is a compound device that automatically creates a USB mass
storage device and a SCSI device as its backend. Unfortunately it lacks
some configuration options that are usually present with a SCSI device,
and cannot represent CD-ROM in particular.

Replace usb-storage with usb-bot, which can be combined with a manually
created SCSI device. libvirt will configure the SCSI device in a way
identical with how QEMU does for usb-storage except that now it respects
a configuration option to represent CD-ROM.

Resolves: https://gitlab.com/libvirt/libvirt/-/issues/368
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Jiri Denemark <jdenemar@redhat.com>