btrfs: test for corruption when reading compressed files

btrfs: test for corruption when reading compressed files

Regression test for read corruption of compressed and shared extents
after punching holes into a file. The same extent is shared by the
same file in consecutive ranges (without other extents in between).

This is motivated by a bug recently found in btrfs for which there
is a patch for the linux kernel titled:

  "Btrfs: fix corruption reading shared and compressed extents after hole
   punching"

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>