xfs: stress XFS delalloc indirect block reservations

xfs: stress XFS delalloc indirect block reservations

This test is based on generic/033, which originally used zero range
operations to reproduce indlen reservation problems. Zero range now
includes a pagecache flush before it updates extents, which means
generic/033 is no longer able to reproduce the problem it was
originally written to test.

Create a new test that uses an XFS-specific mechanism (in DEBUG
mode) to induce delalloc extent splits and reproduce the problem
originally reproduced by generic/033. In addition, update the test
to include a larger buffered write pattern that is known to
reproduce premature indlen exhaustion on delalloc extents.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>