[live snapshot] export bdrv_snapshot_find
[Patch] Refine roms required by running qemu
[live snapshot] allow to accept snapshot name

Usage:

1. start a vm:
qemu-kvm -cpu host -enable-kvm -m 1024 -smp 2 -drive file=/root/vm/winxp/winxp.img,if=none,id=drive0,format=qcow2,cache=directsync -device virtio-blk-pci,scsi=off,drive=drive0,id=disk0 -boot c -monitor stdio

2. take a live snapshot
(qemu) migrate "savevm:snanpshot-1:gzip -c > snapshot-1.gz"

3. load a snapshot
./qemu-kvm -cpu host -enable-kvm -m 1024 -smp 2 -drive file=/root/vm/winxp/winxp.img,if=none,id=drive0,format=qcow2,cache=directsync -device virtio-blk-pci,scsi=off,drive=drive0,id=disk0 -boot c -monitor stdio -incoming "exec: gzip -c -d snapshot-1.gz"