We can't use get_param_value(), it can't handle parameters without
'=' in there.  Examples not working because of that:

  -device foo,id=bar
  -device file=/path/image,format=qcow2,snapshot,id=disk0

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
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