iotests: fix 051.out expected output after error text touchups

iotests: fix 051.out expected output after error text touchups

A patch was recently applied that touched up some error messages that
pertained to key names like 'node-name'. The trouble is it only updated
tests/qemu-iotests/051.pc.out and not tests/qemu-iotests/051.out as
well.

Do that now.

Fixes: 785ec4b1b9 ("block: Clarify error messages pertaining to
'node-name'")
Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
Message-Id: <20210318200949.1387703-2-ckuehl@redhat.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>