Description of problem:
QMP: "DEVICE_TRAY_MOVED" event is emitted twice when eject or change the scsi-cd cdrom, but the IDE cdrom did not meet such issue.
this issue a little different bug 890012 for tray-open value in HMP monitor, but they are all specified the scsi-cd.

Version-Release number of selected component (if applicable):
host info:
# uname -r && rpm -q qemu-kvm
2.6.32-425.el6.x86_64
qemu-kvm-0.12.1.2-2.415.el6.x86_64
guest info:
# uname -r
2.6.32-425.el6.x86_64

How reproducible:
100%

Steps to Reproduce:
1.boot a guest with scsi-cdrom and QMP server.
e.g:...-qmp tcp:0:4444,server,nowait -drive file=/home/my-cdrom1.iso,media=cdrom,if=none,id=drive-disk1,format=raw,cache=none,aio=native -device virtio-scsi-pci,bus=pci.0,addr=0x8,id=scsi0 -device scsi-cd,bus=scsi0.0,drive=drive-disk1,id=disk1
2.connect the QMP server via nc.
$ telnet 10.16.67.29 4444
Trying 10.16.67.29...
Connected to 10.16.67.29.
Escape character is '^]'.
{"QMP": {"version": {"qemu": {"micro": 1, "minor": 12, "major": 0}, "package": "(qemu-kvm-0.12.1.2)"}, "capabilities": []}}
{"execute":"qmp_capabilities"}
{"return": {}}
3.eject and change the scsi-cd cdrom in QMP monitor.
->{"execute":"eject","arguments":{"device":"drive-disk1","force":true}}
->{"execute":"change","arguments":{"device":"drive-disk1","target":"/home/my-cdrom1.iso"}}

Actual results:
after step 3, the "DEVICE_TRAY_MOVED" event is emitted twice when eject or change the scsi-cd cdrom.
->{"execute":"eject","arguments":{"device":"drive-disk1","force":true}}
{"timestamp": {"seconds": 1383190461, "microseconds": 341709}, "event": "DEVICE_TRAY_MOVED", "data": {"device": "drive-disk1", "tray-open": true}}
{"return": {}}
{"timestamp": {"seconds": 1383190462, "microseconds": 525296}, "event": "DEVICE_TRAY_MOVED", "data": {"device": "drive-disk1", "tray-open": false}}
->{"execute":"change","arguments":{"device":"drive-disk1","target":"/home/my-cdrom1.iso"}}
{"timestamp": {"seconds": 1383190469, "microseconds": 910601}, "event": "DEVICE_TRAY_MOVED", "data": {"device": "drive-disk1", "tray-open": true}}
{"timestamp": {"seconds": 1383190469, "microseconds": 910845}, "event": "DEVICE_TRAY_MOVED", "data": {"device": "drive-disk1", "tray-open": false}}
{"return": {}}

Expected results:
the first DEVICE_TRAY_MOVED to open the tray when eject the cdrom, and the second DEVICE_TRAY_MOVED to close the tray when change the cdrom, like:
->{"execute":"eject","arguments":{"device":"drive-disk1","force":true}}
{"timestamp": {"seconds": 1383190461, "microseconds": 341709}, "event": "DEVICE_TRAY_MOVED", "data": {"device": "drive-disk1", "tray-open": true}}
{"return": {}}

->{"execute":"change","arguments":{"device":"drive-disk1","target":"/home/my-cdrom1.iso"}}
{"timestamp": {"seconds": 1383190469, "microseconds": 910845}, "event": "DEVICE_TRAY_MOVED", "data": {"device": "drive-disk1", "tray-open": false}}
{"return": {}}

Additional info: