allow if=none for drive_add
Allow adding unconnected host drives by specifying if=none like it is
possible with -drive. They can be put in use with drive attributes,
like this:
drive_add dummy if=none,id=mydisk,file=/some/disk.img
device_add virtio-blk-pci,drive=mydisk
which is the monitor aequivalent to these command line switches:
-drive if=none,id=mydisk,file=/some/disk.img
-device virtio-blk-pci,drive=mydisk
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>