qemu-iotests: fix 054 cluster size help output

Commit f3f4d2c0 added a hint to increase
the cluster size when a large image cannot be created.  Test 054 now has
outdated output and fails because the golden output does not match.

This patch updates the 054 golden output.
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/054.out

 QA output created by 054
 
 creating too large image (1 EB)
-qemu-img: The image size is too large for file format 'qcow2'
+qemu-img: The image size is too large for file format 'qcow2' (try using a larger cluster size)
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1152921504606846976 
 
 creating too large image (1 EB) using qcow2.py