This new image misses one extent which leads lowmem mode to
allocate new chunks in repair.

Rename original image to no_extent_bad_dev.img.
Because of its bad used bytes, it should let lowmem mode
exclude blocks in repair.

Due to problems of btrfs-image, choose xz as compression tool.

Signed-off-by: Su Yue <suy.fnst@cn.fujitsu.com>