_test_punch the main test function follows the procedure:
- mkfs & mount scratch
- optionally set files extent size hint
- truncate and optionally resvsp
- write or punch to file in specified order at given offsets & lengths
- display the file state (bmap) after each operation
All sizes, offsets and lengths are specified in FS blocks.
Problems may arise on non bash shells due to array usage.
Merge of master-melb:xfs-cmds:29434a by kenmcd.
David Disseldorp