qemu.tests: Add a test for ioeventfd of virtio block device

Do following tests with ioenventfd option for virtio block devie:
  - big file write test
  - reboot
  - iozone
  - poweroff

try with virtio_scsi, ioeventfd works with virtio_scsi 


    bus: pci.0
      type PCI
      dev: virtio-scsi-pci, id "virtio_scsi_pci0"
        ioeventfd = on
        vectors = 4
        indirect_desc = on