Description of problem:
when do live migration with used VHDX format disk, QEMU should be blocked to do live migration and give a message prompt that "Block format 'vhdx' used by device 'drive-data-disk' does not support feature 'live migration".
BTW, tried the vpc format that did not have such issue.

Version-Release number of selected component (if applicable):
host info:
# uname -r && rpm -q qemu-kvm
2.6.32-419.el6.x86_64
qemu-kvm-0.12.1.2-2.402.el6.x86_64
guest info:
2.6.32-419.el6.x86_64

How reproducible:
100%

Steps to Reproduce:
1.create a VHDX format image via Hyper-V.
# qemu-img info /mnt/sluo-data-disk.vhdx
image: /mnt/sluo-data-disk.vhdx
file format: vhdx
virtual size: 2.0G (2147483648 bytes)
disk size: 388M
2.boot guest with VHDX format disk in src and do some read from the VHDX disk.
e.g:...-drive file=/mnt/sluo-data-disk.vhdx,if=none,id=drive-data-disk,format=vhdx,cache=none,werror=stop,rerror=stop,readonly=on -device virtio-blk-pci,bus=pci.0,addr=0x7,drive=drive-data-disk,id=data-disk
guest] # dd if=/dev/vdb of=/dev/null bs=10k
3.boot a dest with incoming mode.
<same-to-src-cli>-incoming tcp:0:5888,server,nowait
4.migration from src to dest and check it.
- src:
(qemu) migrate -d tcp:0:5888
(qemu) info migrate 
Migration status: active
total time: 2229 milliseconds
transferred ram: 70377 kbytes
remaining ram: 1764016 kbytes
total ram: 2113920 kbytes
...
(qemu) info migrate 
Migration status: completed
total time: 18110 milliseconds
downtime: 31 milliseconds
transferred ram: 598047 kbytes
remaining ram: 52 kbytes
total ram: 2113920 kbytes
(qemu) q

-dest:
(qemu) c
(qemu) info status 
VM status: running

Actual results:
after step 4, it can complete migration from src to dest successfully.

Expected results:
QEMU should be blocked to do live migration and give a message prompt that "Block format 'vhdx' used by device 'drive-data-disk' does not support feature 'live migration".

Additional info:
# /usr/libexec/qemu-kvm -M pc -S -cpu SandyBridge -enable-kvm -m 2048 -smp 2,sockets=2,cores=1,threads=1 -no-kvm-pit-reinjection -usb -device usb-tablet,id=input0 -name sluo -uuid 990ea161-6b67-47b2-b803-19fb01d30d30 -rtc base=localtime,clock=host,driftfix=slew -device virtio-serial-pci,id=virtio-serial0,max_ports=16,vectors=0,bus=pci.0,addr=0x3 -chardev socket,id=channel1,path=/tmp/helloworld1,server,nowait -device virtserialport,chardev=channel1,name=com.redhat.rhevm.vdsm,bus=virtio-serial0.0,id=port1 -chardev socket,id=channel2,path=/tmp/helloworld2,server,nowait -device virtserialport,chardev=channel2,name=com.redhat.rhevm.vdsm,bus=virtio-serial0.0,id=port2 -drive file=/mnt/RHEL6.5-20130830.2-Server-x86_64.qcow2,if=none,id=drive-virtio-disk,format=qcow2,cache=none,aio=native,werror=stop,rerror=stop -device virtio-blk-pci,vectors=0,bus=pci.0,addr=0x4,scsi=off,drive=drive-virtio-disk,id=virtio-disk,bootindex=1 -netdev tap,id=hostnet0,vhost=on,script=/etc/qemu-ifup -device virtio-net-pci,netdev=hostnet0,id=virtio-net-pci0,mac=2C:41:38:B6:40:21,bus=pci.0,addr=0x5 -device virtio-balloon-pci,id=ballooning,bus=pci.0,addr=0x6 -global PIIX4_PM.disable_s3=0 -global PIIX4_PM.disable_s4=0 -drive file=/mnt/sluo-data-disk.vhdx,if=none,id=drive-data-disk,format=vhdx,cache=none,werror=stop,rerror=stop,readonly=on -device virtio-blk-pci,bus=pci.0,addr=0x7,drive=drive-data-disk,id=data-disk -k en-us -boot menu=on -vnc :1 -monitor stdio