Fix to eject cdrom on HVM Domain

Fix to eject cdrom on HVM Domain

We tried to eject cdrom(/dev/hdc) on HVM Domain.
But, cdrom media are not ejected from the cdrom device on HostOS.

The module to eject the cdrom device has already been implemented in
qemu-dm.
 But, all devices are opened as raw device for VBD.
Therefore, the module to eject the cdrom device is not work.

The cdrom device was corrected to open as a physical device on HostOS.
When eject is executed on HVM Domain, cdrom media are ejected from the
cdrom device on HostOS.

This patch corrected the problem.
Signed-off-by: Takanori Kasai <kasai.takanori@jp.fujitsu.com>