common: create _test_block_boundaries in common/punch

common: create _test_block_boundaries in common/punch

Create new function _test_block_boundaries() which is testing content of
the blocks after the operation such as zero, or punch hole. The test is
doing the operation around block boundaries to assure correct behaviour
of the operation on block unaligned ranges.

This has been based on test xfs/290 which has been changed to use this
new function. A small change to the output file was required.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>