[Qemu-devel] Run guest-exec request failed in the Windows2012.

[jina]

Hi guys:
Used the guest-exec function, I try to run the windows`s powershell scriptes, 
but the failed.

The cmd and error message:

```

virsh # qemu-agent-command 0e25dcdc-7441-4fc4-8993-4469135a0223 '{"execute": 
"guest-exec", "arguments": {"path": "powershell", "arg": ["-ExecutionPolicy", 
"RemoteSigned", "-NonInteractive", "-File", "C:\\test.ps1"]}}'
error: internal error: unable to execute QEMU agent command 'guest-exec': Guest 
agent command failed, error was 'Failed to execute helper program (Invalid 
argument)'
```

environment:
    - Host system: CentOS7.1
    - Guest system: Windows2012
    - Qemu guest agent version: 2.8.0