If vol-create-from is failed due to 'input volume not found',
virsh outputs like this:
$ sudo virsh vol-create-from testpool test-vol.xml test.img
error: failed to get vol 'test.img', specifying --pool might help
error: Storage volume not found: no storage vol with matching path
However, '--pool' is incorrect because it is already specified as
second argument ('testpool' in this case). It should be "--inputpool".
The patch fixes this by using pooloptname, which will be "inputpool"
in this case and "pool" in other cases, as error message.
6b5c9936ec