qemu-iotests: Fix 128 if sudo required

If passwordless "sudo" works, use it in the qemu-io cmd.
Signed-off-by: NFam Zheng <famz@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/128

@@ -29,6 +29,7 @@ tmp=/tmp/$$
 status=1	# failure is the default!
 
 devname="eiodev$$"
+sudo=""
 
 _setup_eiodev()
 {
@@ -37,6 +38,7 @@ _setup_eiodev()
 		echo "0 $((1024 * 1024 * 1024 / 512)) error" | \
 			$cmd dmsetup create "$devname" 2>/dev/null
 		if [ "$?" -eq 0 ]; then
+			sudo="$cmd"
 			return
 		fi
 	done
@@ -74,7 +76,7 @@ TEST_IMG="/dev/mapper/$devname"
 echo
 echo "== reading from error device =="
 # Opening image should succeed but the read operation should fail
-$QEMU_IO --format "$IMGFMT" --nocache -c "read 0 65536" "$TEST_IMG" | _filter_qemu_io
+$sudo $QEMU_IO --format "$IMGFMT" --nocache -c "read 0 65536" "$TEST_IMG" | _filter_qemu_io
 
 # success, all done
 echo "*** done"