Add a new element to the hardlink test to check we also preseve file
sparseness during the packing process. This should ensure we don't regress this
issue again.
(From OE-Core rev: 0a4e6974b49bf68c4a4098d339b5d655e202a3fd)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>