iotests: Specify qcow2 format for qemu-io in 059

There are two instances of iotest 059 using qemu-io on a qcow2 image. As
of "qemu-iotests: Use qemu-io -f $IMGFMT" the iotests can no longer rely
on $QEMU_IO doing probing, therefore the qcow2 format has to be
specified explicitly here.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NFam Zheng <famz@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/059

@@ -106,8 +106,8 @@ _img_info
 echo
 echo "=== Converting to streamOptimized from image with small cluster size==="
 TEST_IMG="$TEST_IMG.qcow2" IMGFMT=qcow2 IMGOPTS="cluster_size=4096" _make_test_img 1G
-$QEMU_IO -c "write -P 0xa 0 512" "$TEST_IMG.qcow2" | _filter_qemu_io
-$QEMU_IO -c "write -P 0xb 10240 512" "$TEST_IMG.qcow2" | _filter_qemu_io
+$QEMU_IO -f qcow2 -c "write -P 0xa 0 512" "$TEST_IMG.qcow2" | _filter_qemu_io
+$QEMU_IO -f qcow2 -c "write -P 0xb 10240 512" "$TEST_IMG.qcow2" | _filter_qemu_io
 $QEMU_IMG convert -f qcow2 -O vmdk -o subformat=streamOptimized "$TEST_IMG.qcow2" "$TEST_IMG" 2>&1
 
 echo