[QEMU 'blockdev-add' with 'node-name']

Tested with: v2.6.0-1025-g38f1ffb

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$ qemu-img create -f qcow2 backup2.qcow2 1G
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 $ socat UNIX:/export/qemu-backup-tests/qmp-sock READLINE,history=$HOME/.qmp_history,prompt='QMP> '
{"QMP": {"version": {"qemu": {"micro": 50, "minor": 6, "major": 2}, "package": " (v2.6.0-1025-g38f1ffb)"}, "capabilities": []}}
QMP>
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QMP> {"execute":"qmp_capabilities"}
{"return": {}}
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QMP> { "execute": "blockdev-add",
       "arguments": { "options" : { "driver": "qcow2", 
                                    "id": "drive-ide2-0-0",
                                    "file": { "driver": "file",
                                              "filename": "/home/kashyapc/tinker-space/qemu-upstream/scripts/qmp/backup2.qcow2",
                                              "node-name": "node-backup2" } } } }
{"return": {}}
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(qemu) info block
drive-ide0-0-0 (#block127): ./cirros-0.3.3.qcow2 (qcow2)
    Cache mode:       writeback

drive-ide3-0-0 (#block322): /tmp/test3.raw (raw)
    Removable device: not locked, tray closed
    Cache mode:       writeback

drive-ide2-0-0 (#block1351): /home/kashyapc/tinker-space/qemu-upstream/scripts/qmp/backup2.qcow2 (qcow2)
    Removable device: not locked, tray closed
    Cache mode:       writeback
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QMP> { "execute": "blockdev-backup", 
       "arguments": {
         "device": "drive-ide0-0-0", 
         "target": "node-backup2", 
         "sync": "full" }}
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[Error with 'node-name':]

QMP> { "execute": "blockdev-backup", 
QMP>        "arguments": {
QMP>          "device": "drive-ide0-0-0", 
QMP>          "target": "node-backup2", 
QMP>          "sync": "full" }}
{"return": {}}
{"timestamp": {"seconds": 1466159490, "microseconds": 620827}, "event": "BLOCK_JOB_ERROR", "data": {"device": "drive-ide0-0-0", "operation": "write", "action": "report"}}
{"timestamp": {"seconds": 1466159490, "microseconds": 620913}, "event": "BLOCK_JOB_COMPLETED", "data": {"device": "drive-ide0-0-0", "len": 41126400, "offset": 196608, "speed": 0, "type": "backup", "error": "Input/output error"}}
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