expand 252 with more corner case tests

expand 252 with more corner case tests

This patch adds additional punch hole tests to 252
that were used to test ext4 punch hole. The _test_generic_punch
routine has been modified to accept two new flags:

-k To keep the test file between tests.
   This will test the handling of existing holes

-d To not sync the file between tests.
   This will test the handling of delayed extents

Four new corner cases have also been added to the routine:
14. data -> hole @ EOF
15. data -> hole @ 0
16. data -> cache cold ->hole
17. data -> hole in single block file

Signed-off-by: Allison Henderson <achender@us.ibm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>