Description of problem:
qemu-kvm ignores virtio-scsi cdrom as a boot device

Version-Release number of selected component (if applicable):
qemu-kvm-1.5.3-19.el7.x86_64
seavgabios-bin-1.7.2.2-4.el7.noarch
seabios-bin-1.7.2.2-4.el7.noarch
sgabios-bin-0.20110622svn-3.el7.noarch

How reproducible:
always

Steps to Reproduce:
1. define libvirt domain with virtio-scsi cdrom such as:
    <disk type='file' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <source file='/path/to/image.iso'/>
      <target dev='sdb' bus='scsi'/>
      <readonly/>
    </disk>
2. define either <boot order='$INT'/> element within disk element or <boot dev='cdrom'/> within <os> element
3. boot the VM

Actual results:
boot from cdrom is not mentioned, when I enable bootmenu, it doesn't show up there

Expected results:
VM boots from virtio-scsi disk

Additional info: