iotests: Fix test 128 for password-less sudo

As of 934659c4, $QEMU_IO is generally no
longer a program name, and therefore "sudo -n $QEMU_IO" will no longer
work.

Fix this by copying the qemu-io invocation function from common.config,
making it use $sudo for invoking $QEMU_IO_PROG, and then use that
function instead of $QEMU_IO.
Reported-by: NFam Zheng <famz@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/128

@@ -31,6 +31,11 @@ status=1	# failure is the default!
 devname="eiodev$$"
 sudo=""
 
+_sudo_qemu_io_wrapper()
+{
+    (exec $sudo "$QEMU_IO_PROG" $QEMU_IO_OPTIONS "$@")
+}
+
 _setup_eiodev()
 {
 	# This test should either be run as root or with passwordless sudo
@@ -76,7 +81,9 @@ TEST_IMG="/dev/mapper/$devname"
 echo
 echo "== reading from error device =="
 # Opening image should succeed but the read operation should fail
-$sudo $QEMU_IO --format "$IMGFMT" --nocache -c "read 0 65536" "$TEST_IMG" | _filter_qemu_io
+_sudo_qemu_io_wrapper --format "$IMGFMT" --nocache \
+                      -c "read 0 65536" "$TEST_IMG" \
+    | _filter_qemu_io
 
 # success, all done
 echo "*** done"